Minor Performance

- Clear image cache if necessary (prevent clearing if the downloaded data is not image)
- Cache missing cards (prevent finding missing cards unless the user has fetched/downloads an image)
- Clear preselected options for New Gauntlet Match (easier to filter decks for Gauntlet)

forge-gui-desktop/src/main/java/forge/GuiDesktop.java

@@ -290,6 +290,7 @@ public class GuiDesktop implements IGuiBase {
     @Override
     public void clearImageCache() {
         ImageCache.clear();
+        ImageKeys.clearMissingCards();
     }
 
     @Override

forge-gui-desktop/src/main/java/forge/ImageCache.java

@@ -96,6 +96,7 @@ public class ImageCache {
     public static void clear() {
         _CACHE.invalidateAll();
         _missingIconKeys.clear();
+        ImageKeys.clearMissingCards();
     }
 
     /**