Reject request when any unknown flag is speficied

Currently EditableInputConnection#requestUpdateCursorAnchorInfo
never returns false unless InputMethodManager is somehow
unavailable.

This is problematic, especifially when we add a new flag to
EditableInputConnection#requestUpdateCursorAnchorInfo in a
future release.

With this CL, #requestUpdateCursorAnchorInfo does nothing and
immediately returns false when one ore more unknown bits are
specified.

BUG: 17324806
Change-Id: I5601714b481e8efa0ad3337c0d093cfcf55eade3