ap_rgetline(): completely ignore an empty bucket... previously the logic

               generally worked but with a memory debug build it could
               crash since some memory debuggers don't like an alloc of
               zero bytes


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93037 13f79535-47bb-0310-9956-ffa450edef68