android imm.isAcceptingText() crash fix

[AlexDochioiu]

I see some isolated cases where isAcceptingText crashes, killing the entire app. Added a small safety net to avoid this.

P.s. This was fully reproducible for one user (Huawei P30 light - Android 10) when accessing app.dexhunter.io.

[pichillilorenzo]

The Fixed canGoForward NPE commit should be made in a separate pull request.
By the way, I think that the null pointer exception on canGoForward is caused by the usage of the webview controller after the webview as been disposed.
Probably, I should throw an exception if someone tries to call any controller method after the webview is disposed, because the internal _channel will be null.

[pichillilorenzo]

@all-contributors please add @AlexDochioiu for code

[allcontributors]

@pichillilorenzo

I've put up a pull request to add @AlexDochioiu! 🎉