mxqd: Avoid user sort when server is full

Avoid sorting the user list when we are not going to start a job anyway.
Also save a few source lines and remove a dead initalization.

mxqd.c

@@ -1510,34 +1510,22 @@ static void move_user_to_end(struct mxq_server *server, struct mxq_user_list *us
 
 long start_user_with_least_running_global_slot_count(struct mxq_server *server)
 {
-    struct mxq_user_list *ulist;
-    unsigned long slots_started = 0;
-    unsigned long slots_free;
-    int waiting = 0;
-    unsigned long df_scratch;
-
-    assert(server);
-
-    if (!server->user_cnt)
+    unsigned long slots_free = server->slots - server->slots_running;
+    if (!server->user_cnt || !slots_free)
         return 0;
-
     server_sort_users_by_running_global_slot_count(server);
-    slots_free = server->slots - server->slots_running;
-
-    if (!slots_free)
-        return 0;
-
-    df_scratch=mx_df(MXQ_JOB_TMPDIR_FS "/.");
+    unsigned long df_scratch=mx_df(MXQ_JOB_TMPDIR_FS "/.");
+    int waiting = 0;
 
-    for (ulist = server->users; ulist; ulist = ulist->next) {
+    for (struct mxq_user_list *ulist = server->users; ulist; ulist = ulist->next) {
         /* if a previous user is waiting for free resources, don't start jobs
          * for later users. */
         if (waiting && can_start_job_for_user(ulist, df_scratch, server, slots_free))
             /* returning -1 here tells the daemon to set its status in the
              * database to WAITING, which is just informational.  */
             return -1;
 
-        slots_started = start_user(ulist, slots_free, df_scratch);
+        unsigned long slots_started = start_user(ulist, slots_free, df_scratch);
         if (slots_started) {
             /* move user to end of list so that we get a round-robin with with
              * other users which sort to the same precedence. */