Fixes regression introduced by 35c8f15bc67f7602438fe0c39a69ff6ddf6b8297
Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=55215
We already test for an invalid pointer, those tests don't really help. The test against DrawTextA crashes on windows sometimes, the other test shows that windows probably just overruns the stack variable: `textheight = DrawTextExA((HDC)0xdeadbeef, (LPSTR)0xdeadbeef, 100, &rect, 0, 0);`