[Bug 43536] WIC can't encode to GUID_WICPixelFormat32bppPBGRA PNG

https://bugs.winehq.org/show_bug.cgi?id=43536

--- Comment #2 from Anton Romanov  ---
So, this happens since app renders to PNG specifying
GUID_WICPixelFormat32bppPBGRA pixelformat and wine's windowscodesc does not
support that and falls back to RGB and loses alpha channel completely
If I just add 
{&GUID_WICPixelFormat32bppPBGRA, 32, 8, PNG_COLOR_TYPE_RGB_ALPHA, 0, 1},

to png_pixelformats in pngformat.c then it all works perfectly

(though only because all pictures it uses have either 0 or 255 alpha)