SDL_BlitScaled: prevent crash if dest width or height is 0

src/video/SDL_stretch.c

@@ -260,6 +260,10 @@ SDL_UpperSoftStretch(SDL_Surface * src, const SDL_Rect * srcrect,
         dstrect = &full_dst;
     }
 
+    if (dstrect->w == 0 || dstrect->h == 0) {
+        return 0;
+    }
+
     /* Lock the destination if it's in hardware */
     dst_locked = 0;
     if (SDL_MUSTLOCK(dst)) {