Fix a bug where the cache would be out of sync

During recorrection, the cursor position when calling
commitText is not necessarily at the end of the
composing text.
Besides, RichInputConnection assumes the cursor is
always after any composing text. This is not correct,
but in the practice, it seems all code paths work.
We should fix this in the future.

Bug: 13060691
Change-Id: I15f71fff62d36e80cf6e4a022c5e78af634b199d