Missed one

svn-id: r8536

backends/sdl/sdl_gl.cpp

@@ -294,6 +294,8 @@ void OSystem_SDL_OpenGL::hotswap_gfx_mode() {
 	if (!_screen)
 		return;
 
+	StackLock lock(_mutex); // Lock the mutex until this function ends
+
 	// Keep around the old _screen & _tmpscreen so we can restore the screen data
 	// after the mode switch.
 	SDL_Surface *old_screen = _screen;