ap_regex: Follow up to r1897244: Fix pmatch overflow and returned value at limits.

Don't write to pmatch[nlimit:] when ncaps > nlimit, rc should not exceed nmatch
either as before r1897244.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1897248 13f79535-47bb-0310-9956-ffa450edef68
