[android crash] Fix exception when animating region during initialization

[mlanter]

Fixes a crash cause by calling animateToRegion on the map while it is still be initialized.

To reproduce:
In the componentDidMount of the component that renders the MapView add a this._map.animateToRegion(region, 1500);.

Basically on the native side we haven't initialized the map variable yet (which happens in onMapReady) so if that's the case we can't do an animateToRegion yet.

[mlanter]

cc: @spikebrehm

[spikebrehm]

Released as v0.12.3