Only blit neutral surfaces.

On the Mac loaded images are not in the neutral format causing rendering
glitches when using blit_surface using these images. Test and when
needed convert the image before using it.

Fixes bug #22045.

changelog

@@ -1,4 +1,6 @@
 Version 1.11.14+dev:
+ * Graphics:
+   * Fixed bug #22045: Only blit neutral surfaces.
  * Language and i18n:
    * Updated translations: Portuguese
  * Miscellaneous and bug fixes:
@@ -12,7 +14,6 @@ Version 1.11.14+dev:
    * Fix bug #22020: make base units with variations help entry clickable
      from the 'Unit Description' menu entry or from side pane.
 
-
 Version 1.11.14:
  * Campaigns:
    * Son of the Black Eye: minor balance tweaks to scenarios 7, 8 and 14

src/sdl_utils.cpp

@@ -1892,12 +1892,14 @@ surface create_compatible_surface(const surface &surf, int width, int height)
 	return s;
 }
 
-void blit_surface(const surface& src,
+void blit_surface(const surface& surf,
 	const SDL_Rect* srcrect, surface& dst, const SDL_Rect* dstrect)
 {
-	assert(src);
+	assert(surf);
 	assert(dst);
 
+	const surface& src = is_neutral(surf) ? surf : make_neutral_surface(surf);
+
 	// Get the areas to blit
 	SDL_Rect dst_rect = create_rect(0, 0, dst->w, dst->h);
 	if(dstrect) {