OS2_VideoInit: zero the stSDLDisplay and stSDLDisplayMode variables

Fixes testdisplayinfo.exe crashing in SDL2-2.0.13.  (How it did work before?..)
diff --git a/src/video/os2/SDL_os2video.c b/src/video/os2/SDL_os2video.c
index 662c67f..60c112a 100644
--- a/src/video/os2/SDL_os2video.c
+++ b/src/video/os2/SDL_os2video.c
@@ -1555,6 +1555,8 @@
       return SDL_SetError( "Video mode query failed." );
     }
 
+    SDL_zero(stSDLDisplay); SDL_zero(stSDLDisplayMode);
+
     stSDLDisplayMode.format = _getSDLPixelFormat( stVOInfo.ulBPP,
                                                   stVOInfo.fccColorEncoding );
     stSDLDisplayMode.w = stVOInfo.ulHorizResolution;