log core: fix the new piped logger case where we couldn't connect

the replacement stderr logger's stderr to the NULL stdout stream.  
Continue in this case, since the previous alternative of no error 
logging at all (/dev/null) is far worse. [William Rowe]

also disambiguate an error message to diagnose future error reports

Backport: r568326, r568322


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@569542 13f79535-47bb-0310-9956-ffa450edef68