Clear thumbnail when saving changes. Not sure this is the best place

to do it, but it fixes the problem I'm after.

xwords4/android/XWords4/src/org/eehouse/android/xw4/GameConfigDelegate.java

@@ -1156,6 +1156,7 @@ public class GameConfigDelegate extends DelegateBase
             GameLock gameLock = new GameLock( m_rowid, true ).lock();
             GameUtils.applyChanges( m_activity, m_gi, m_car, gameLock, 
                                     forceNew );
+            DBUtils.saveThumbnail( m_activity, gameLock, null ); // clear it
             gameLock.unlock();
         }
     }