Fixed potential crash in mapView's animationDidStop:finished:context:

In this method there was the following lines of code:

```objective-c
for (ADClusterAnnotation * annotation in self.annotations) {
      if (![annotation isKindOfClass:[MKUserLocation class]]) {
            if (annotation.shouldBeRemovedAfterAnimation) {
                [annotation reset];
            }
            annotation.shouldBeRemovedAfterAnimation = NO;
      }
}
```

But sometimes self.annotations contains objects of class "MKTeleportingUserLocation" (which is only a child of NSObject and not of MKUserLocation) and so on. So I changed this if-statement from blacklist- to whitelist-method:

```objective-c
for (ADClusterAnnotation * annotation in self.annotations) {
      if ([annotation isKindOfClass:[ADClusterAnnotation class]]) {
            if (annotation.shouldBeRemovedAfterAnimation) {
                [annotation reset];
            }
            annotation.shouldBeRemovedAfterAnimation = NO;
      }
}
```