SDL_GetCSSCursorName: Don't assert on unrecognized cursor types.

These values are passed through from the calling app and shouldn't trigger
asserts when they are bogus.

src/video/SDL_video.c

@@ -5573,7 +5573,6 @@ const char *SDL_GetCSSCursorName(SDL_SystemCursor id, const char **fallback_name
         return "w-resize";
 
     default:
-        SDL_assert(0);
         return "default";
     }
 }