Fix a storage leak in mod_mime_magic.

Trivial to reproduce:

. enable mod_mime_magic
. copy "apache_pb.gif" to "picturefile"
. set breakpoint in magic_rsl_printf()
. request "picturefile"


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90466 13f79535-47bb-0310-9956-ffa450edef68