fix: added Method Channel result response to null

[Javidroid]

Apart from code format changes, the most important change is adding result?.success(null) to the else block of onActivityResult(...) method on Dialog.kt

This causes the MethodChannel result to return something that can be 'heard' from the outside. In this case: null.

It is specifically a 'success' instead of an 'error' as, technically, the operation was made correctly, but the user chose to cancel it, returning nothing instead.

[incrediblezayed]

👍🏻 Thanks