Fix a crash when flickering in onComplete

flixel/effects/FlxFlicker.hx

@@ -182,7 +182,12 @@ class FlxFlicker implements IFlxDestroyable
 			{
 				completionCallback(this);
 			}
-			release();
+
+			// NOTE: Calling `flicker` in the completion callback will call release() on this object before reinstantiating it.
+			// If that happens, we don't want to call release() again! So we check if the flicker is still done before releasing.
+			if (this.timer == Timer) {
+				release();
+			}
 		}
 	}