Prevent crashes and related issues if initial activity is destroyed on Android

Prevent crashes and related issues if initial activity is destroyed on Android

* java/org/gnu/emacs/EmacsWindow.java
(EmacsWindow) <initialWindowCreated>: New variable.
(EmacsWindow): If the initial frame has not yet been created,
set attachmentToken to -1.

* java/org/gnu/emacs/EmacsWindowManager.java (registerWindow):
When the window's attachment token is -1 (i.e., it is the
default window), start EmacsActivity rather than
EmacsMultitaskActivity.  Catch exceptions around startActivity.