Merge r1775775 from trunk:

mod_proxy_{ajp,fcgi}: Fix a possible crash when reusing an established
backend connection, happening with LogLevel trace2 or higher configured,
or at any log level with compilers not detected as C99 compliant (e.g.
MSVC on Windows).


Submitted by: ylavic
Reviewed by: ylavic, jim, covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1777975 13f79535-47bb-0310-9956-ffa450edef68