Merge r1666361 from trunk:

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
Submitted by: jailletc36
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1670319 13f79535-47bb-0310-9956-ffa450edef68