re-expand bundle if caches directory has been cleared

Is there a cheaper way to make this check? Could we (say) just look for the existence of the `bundlePath`, rather than enumerating the contents? I ask because I can easily see this being used in contents in which is it expected to be cheap. E.g.

```objective-c
for(NSString *name in @[@"a.png", @"b.png" /* ... */]) {
  UIImage *image = [[BaledBundle NSBundle] imageNamed:name];
  // do something with image
}
```