GUI: insert 100ms delay when minimized

issue #220

src/gui/gui.cpp

@@ -17,6 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#include <SDL_video.h>
 #define _USE_MATH_DEFINES
 #include "gui.h"
 #include "util.h"
@@ -5350,6 +5351,10 @@ bool FurnaceGUI::loop() {
       commitSettings();
       willCommit=false;
     }
+
+    if (SDL_GetWindowFlags(sdlWin)&SDL_WINDOW_MINIMIZED) {
+      SDL_Delay(100);
+    }
   }
   return false;
 }