Update MainWindow.java

Found a crash while running app in Samsung Tab 3 and it shows Null pointer exception for the cursor in loadUnreadCounters method so added condition to check cursor is null or not.And after adding it is working fine.
Explicitly set style of the new status spinner.

This should fix white-on-gray text on Android 2.3.
fix crash when entering @ as a JID
chat window: finally fix 'OK' btn alignment
remove unused action bar pngs
smackable: implement upsertRoster
XEP-0198: increase buffers, unblock tcp!