Fixed memory leak when removing existing displays

(cherry picked from commit cfc7cac3c9)

src/video/SDL_video.c

@@ -623,6 +623,7 @@ void SDL_DelVideoDisplay(int index)
     SDL_SendDisplayEvent(&_this->displays[index], SDL_DISPLAYEVENT_DISCONNECTED, 0);
 
     if (index < (_this->num_displays - 1)) {
+        SDL_free(_this->displays[index].driverdata);
         SDL_memmove(&_this->displays[index], &_this->displays[index + 1], (_this->num_displays - index - 1) * sizeof(_this->displays[index]));
     }
     --_this->num_displays;