Fix suexec segfault when group doesn't exist.

Submitted by:	Gregory Neil Shapiro <gshapiro@wpi.edu>
Reviewed by:	Randy, Dean, Roy


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@78003 13f79535-47bb-0310-9956-ffa450edef68