bareos-sd: close network connection if job isn't started

If the Director tries to start a new job on the SD, the SD checks,
if the MaximumConcurrentJobs criteria meet. If not, no new job is
started.
This fix will close the network connection.

Fixes #763: some Backups fail after 605 seconds in a schedule of 170 server

src/stored/dir_cmd.c

@@ -230,6 +230,7 @@ void *handle_director_connection(BSOCK *dir)
 
    if (!count_running_jobs()) {
       Emsg0(M_ERROR, 0, _("Number of Jobs exhausted, please increase MaximumConcurrentJobs\n"));
+      dir->signal(BNET_TERMINATE);
       return NULL;
    }