(POS_AS_IN_BUFFER): Add 1 only if operating on a buffer.

(POS_AS_IN_BUFFER): Add 1 only if operating on a buffer.
(re_match_2, re_search_2): Adjust startpos or pos by 1
only if acting on a buffer.
nil for re_match_object means a buffer.
(re_match_2_internal <notwordbeg>): Assume POS1 is positive.