Bug fix for NullPointerException Error at LoginFragment

[BernaTasel]

Fixed error when trying to login while textfields are null.

Complete with the least possible changes with your suggestion.

[turkergoksu]

I manage to get all of the available error messages inside Validator classes and logged in successfully. Looks like it's fixed. @BernaTasel 👏

[bariscankurt]

I checked required control cases and everything is working as expected. Congrats 👏

[safaorhan]

Thanks to all of you folks!