[PATCH 0/1] MR7700: gdiplus: Avoid storing NULL in gdip_font_link_section.

[Eric Tian (＠thdaemon)]

In `generate_font_link_info`, because the return value of
`GdipCreateFontFromDC` is not checked, section->font might be set to NULL.
`GdipMeasureString` calls `gdip_format_string`, which then calls
`generate_font_link_info` and `font_link_get_text_extent_point`. In
`font_link_get_text_extent_point`, the font from `gdip_font_link_section` is also
not checked for NULL, which may cause a crash.

Therefore, in `generate_font_link_info`, when `GdipCreateFontFromDC` fails,
store `(GpFont *)base_font` (as with `IMLangFontLink_MapFont` failure) to ensure
the font in `gdip_font_link_section` is valid.

---

This issue was reproduced while using the [QQ Music](https://y.qq.com/download/index.html).
Below is the original winedbg log (on Wine 10.4 + wine-staging + DXVK, 
with some native libraries used. If needed and permitted by WineHQ, I will list them.)
(PS: This issue should also be reproduced using generic wine master without third parties)

```
Wine-dbg>frame 1
Wine-dbg>bt
Backtrace:
  0 0x00000078ed4d58 get_font_hfont+0x30(graphics=<couldn't compute location>, font=<couldn't compute location>, format=<couldn't compute location>, hfont=<couldn't compute location>, lfw_return=<couldn't compute
 location>, matrix=<couldn't compute location>) [/home/up/wine/build32/../wine/dlls/gdiplus/graphics.c:2476] in gdiplus (0x0000000073f700)
=>1 0x00000078ed21bd font_link_get_text_extent_point+0xb9(info=000000000073F774, index=0, length=0xb, max_ext=0x7fffff83, fit=000000000073F7CC, size=000000000073F7B0) [/home/up/wine/build32/../wine/dlls/gdiplus/g
raphics.c:5537] in gdiplus (0x0000000073f74c)
  2 0x00000078ed340d gdip_format_string+0x2f9(graphics=0000000003665DD0, hdc=0000000034010075, string=L"Q音听我想听的歌???", length=0xb, font=0000000003672700, rect=000000000073F864, format=0000000009FEB508, ignore_empt
y_clip=0x1, callback=0000000078EDADC8, user_data=000000000073F878) [/home/up/wine/build32/../wine/dlls/gdiplus/graphics.c:5663] in gdiplus (0x0000000073f81c)
  3 0x00000078ea8283 GdipMeasureString+0x3cb(graphics=<couldn't compute location>, string=<couldn't compute location>, length=<couldn't compute location>, font=<couldn't compute location>, rect=<couldn't compute 
location>, format=<couldn't compute location>, bounds=<couldn't compute location>, codepointsfitted=<couldn't compute location>, linesfilled=<couldn't compute location>) [/home/up/wine/build32/../wine/dlls/gdiplu
s/graphics.c:6050] in gdiplus (0x0000000073f8c0)
  4 0x00000077d41fd2 in qqmusic (+0x31fd2) (0x0000000073f908)
  5 0x00000077d3e1c6 in qqmusic (+0x2e1c6) (0x0000000073f96c)
  6 0x00000077d3dd11 in qqmusic (+0x2dd11) (0x0000000073f9f8)
  7 0x00000077f29bd4 in qqmusic (+0x219bd4) (0x0000000073fa70)
  8 0x00000077f29a63 in qqmusic (+0x219a63) (0x0000000073faa0)
  9 0x00000077f28760 in qqmusic (+0x218760) (0x0000000073fb08)
  10 0x00000077b059d7 in common (+0x1059d7) (0x0000000073fb94)
  11 0x00000077b06c35 in common (+0x106c35) (0x0000000073fbc8)
  12 0x0000007a038b48 in user32 (+0x8b48) (0x0000000073fbf8)
  13 0x0000007a093e43 call_window_proc+0xa7(hwnd=0000000000060138, msg=0x113, wp=0x400, lp=0, result=000000000073FC68, arg=0000000077B06B90) [/home/up/wine/build32/../wine/dlls/user32/winproc.c:111] in user32 (0x
0000000073fc40)
  14 0x0000007a09c066 dispatch_win_proc_params+0xce(params=000000000073FCA0) [/home/up/wine/build32/../wine/dlls/user32/winproc.c:710] in user32 (0x0000000073fc7c)
  15 0x0000007a09be4a dispatch_message+0x9e(msg=000000000073FDCC, ansi=0) [/home/up/wine/build32/../wine/dlls/user32/message.c:804] in user32 (0x0000000073fcd8)
  16 0x0000007a04f530 DispatchMessageW+0xff(msg=000000000073FDCC) [/home/up/wine/build32/../wine/dlls/user32/message.c:890] in user32 (0x0000000073fd60)
  17 0x000000780c001d in qqmusic (+0x3b001d) (0x0000000073fe38)
  18 0x000000780c0ce6 in qqmusic (+0x3b0ce6) (0x0000000073fea8)
  19 0x00000000403af4 in qqmusic (+0x3af4) (0x0000000073fefc)
  20 0x00000000403bd6 in qqmusic (+0x3bd6) (0x0000000073ff50)
  21 0x0000007bcdeb10 in kernel32 (+0xeb10) (0x0000000073ff68)
  22 0x0000007be0d083 in ntdll (+0xd083) (0x0000000073ff78)
  23 0x0000007be435b2 call_thread_func+0x2e(entry=000000000040678E, arg=00000000003F1000) [/home/up/wine/build32/../wine/dlls/ntdll/signal_i386.c:526] in ntdll (0x0000000073ffec)
Wine-dbg>info locals
0x00000078ed21bd font_link_get_text_extent_point+0xb9: (0073f74c)
        struct gdip_format_string_info* info=000000000073F774 (parameter [EBP+8])
        INT index=0 (parameter [EBP+12])
        int length=0xb (parameter [EBP+16])
        int max_ext=0x7fffff83 (parameter [EBP+20])
        LPINT fit=000000000073F7CC (parameter [EBP+24])
        SIZE* size=000000000073F7B0 (parameter [EBP+28])
        DWORD to_measure_length=0x3 (local [EBP-16])
        HFONT hfont=000000000D0A00AE (local [EBP-24])
        HFONT oldhfont=000000004C0A00B0 (local [EBP-20])
        SIZE sizeaux={cx=0x7c, cy=0x13} (local [EBP-32])
        int i=0x8 (local [EBP-8])
        int fitaux=0x8 (local [EBP-36])
        struct gdip_font_link_section* section=00000000037E31A8 (local [EBP-12])
Wine-dbg>p *section

Exception c0000005
Wine-dbg>x/10x 0x00000000037E31A8
0x000000037e31a8:  0073f78c 037e3188 00000008 0000000b
0x000000037e31b8:  00000000 00000000 00000004 8146001b
0x000000037e31c8:  78e0c030 78e0c030
```