core: For consistency, ensure that read lines are NUL terminated on any

error, not only on buffer full.
trunk patch: http://svn.apache.org/r1824303
+1: ylavic, rpluem, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1824469 13f79535-47bb-0310-9956-ffa450edef68