Added EDT guard to ImageCache.getImage to track down possible reasons for http://www.slightlymagic.net/forum/viewtopic.php?p=114857#p114857

src/main/java/forge/ImageCache.java

@@ -197,6 +197,7 @@ public class ImageCache {
      * Returns the Image corresponding to the key.
      */
     private static BufferedImage getImage(final String key) {
+        FThreads.assertExecutedByEdt(true);
         try {
             return ImageCache._CACHE.get(key);
         } catch (final ExecutionException ex) {