monitor: fix qmp_getfd() fd leak in error case

qemu_chr_fe_get_msgfd() transfers ownership of the file descriptor to
the caller.  Therefore all code paths in qmp_getfd() should either
register the file descriptor somewhere or close it.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

monitor.c

@@ -2228,6 +2228,7 @@ void qmp_getfd(const char *fdname, Error **errp)
     }
 
     if (qemu_isdigit(fdname[0])) {
+        close(fd);
         error_set(errp, QERR_INVALID_PARAMETER_VALUE, "fdname",
                   "a name not starting with a digit");
         return;