Avoid a potential integer underflow in the lock timeout value sent back to a...

Avoid a potential integer underflow in the lock timeout value sent back to a client. The answer to a LOCK request could be an extremly large integer if the time needed to lock the resource was longer that the requested timeout given in the LOCK request. In such a case, we now answer "Second-0".  PR55420

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1666361 13f79535-47bb-0310-9956-ffa450edef68