bflibrary: Make SDL1 mode checking accept SVGA/XGA res

The SDL1 video mode availability verification was given too much
authority - it could reject a mode if entering it requires
additional blitting. We cannot allow that when any remade
Bullfrog games will use these resolutions by default.

This change forces the library to try to cope with 640x400 and
640x480, even if it marks these modes as not available.

Author: mefistotelis

bflibrary/src/x86-win-sdl/sscreen.c

@@ -672,13 +672,29 @@ TbBool LbHwCheckIsModeAvailable(TbScreenMode mode)
         SDL_FreeSurface(draw_surface);
     }
 
-    closestBPP = SDL_VideoModeOK(mdinfo->Width, mdinfo->Height,
-      mdinfo->BitsPerPixel, sdlFlags);
+    closestBPP = SDL_VideoModeOK(mdWidth, mdHeight, mdinfo->BitsPerPixel, sdlFlags);
+
+    if ((closestBPP == 0) && (mdWidth == 640) && ((mdHeight == 400) || (mdHeight == 480)) &&
+      ((mdinfo->BitsPerPixel == 8) || (mdinfo->BitsPerPixel == 24)))
+    {
+        // The 640x400 and 640x480 must always be available, even if SDL will need to cheat to achieve that
+        closestBPP = 24;
+    }
 
     // Even if different colour depth is returned, as long as the value is
     // non-zero, SDL can simulate any bpp with additional internal surface
     firstSurfaceOk = (closestBPP != 0);
 
+    if (!firstSurfaceOk || !secondSurfaceOk)
+    {
+        const char *reason = NULL;
+        if (!firstSurfaceOk)
+            reason = "SDL says the mode is not OK";
+        if (!secondSurfaceOk)
+            reason = "cannot create second surface";
+        LOGDBG("Mode %s unavailable - %s", mdinfo->Desc, reason);
+    }
+
     return firstSurfaceOk && secondSurfaceOk;
 }