v0.6.4: various bugfixes:

- fixed corrupted mimics causing save/load crashes
- fixed crashes when destroy is called on the same group twice
- syncronized texture cache methods
- added safety checks to
  - SummoningTrap
  - WaterOfHealth
  - WndAlchemy
  - WndBag

SPD-classes/src/main/java/com/watabou/noosa/Group.java

@@ -51,8 +51,10 @@ public class Group extends Gizmo {
 			}
 		}
 		
-		members.clear();
-		members = null;
+		if (members != null) {
+			members.clear();
+			members = null;
+		}
 		length = 0;
 	}