Add info to debug logging.

Avoid null pointer dereference by returning if we can't get
a lua VM.
Move "we got a VM" message to after we know we have one.
Check that we found the lua handler function before trying to
call it.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@939987 13f79535-47bb-0310-9956-ffa450edef68