ab: Fix potential buffer overflows when processing the T and X
    command-line options.

PR: 55360
Submitted by: Mike Rumph <mike.rumph oracle.com>
Reviewed by: trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1510707 13f79535-47bb-0310-9956-ffa450edef68