Fixed memory leak in software YUV stretch code

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%4010

src/video/SDL_yuv_sw.c

@@ -1299,6 +1299,9 @@ void SDL_FreeYUV_SW(_THIS, SDL_Overlay *overlay)
 
 	swdata = overlay->hwdata;
 	if ( swdata ) {
+		if ( swdata->stretch ) {
+			SDL_FreeSurface(swdata->stretch);
+		}
 		if ( swdata->pixels ) {
 			free(swdata->pixels);
 		}