Use stable item ID instead of URI for checkedItem

This is faster, more correct, and also harder to get wrong. And it was
wrong, there were quite common situations where the previous code
threw CursorIndexOutOfBoundsException because getRingtonePosition()
called getItemId() which called... getRingtonePosition() again.

CC Bug: 30658854
Test: monkeytest: crashed this before; now we are crash-free.

Change-Id: I68c06f2123fb84c15d4bbadec7be61c5cdfd1da7
1 file changed