Android issue for multiple modals

my current version: v2.4.0

Attached the screenshots, on testing with the example.

If we close the modal by pressing android back button instead of the close button, warning message will be shown when we open another modal.

After quick checking on source code, I made the following workaround, but I am not sure if it will break other behaviour.

  _close = async () => {
    if (this.state.isVisible) {
      this.backdropRef.transitionTo({ opacity: 0 }, this.props.backdropTransitionOutTiming);
      this.contentRef[this.props.animationOut](this.props.animationOutTiming).then(() => {
        this.setState({ isVisible: false });
        this.props.onModalHide();
      });
    }
  };

[mmerickel]

I do not think this is directly related to the back button. Rather if isVisible gets toggled quickly while transitioning occurs some pretty bad things happen.

1. The refs gets nulled out temporarily which can cause the backdropRef and/or contentRef to be null which causes the promise rejection seen above. Semi-related is this issue https://github.com/facebook/react/issues/4533 but the real issue is just that _close is called while already closing and/or opening.

2. The visible prop may be set to false on the native Modal component while transitioning which causes setState to be called on an unmounted component error inside the animated View.

[mmazzarolo]

@ccycecilyip could you give a shot to @mmerickel solution? Thanks!