mxq_job: Fix invalid pointer deref on error path

mxq_job.c

@@ -284,7 +284,7 @@ uint64_t mxq_select_job_from_group(struct mx_mysql *mysql, uint64_t group_id)
     struct mx_mysql_bind param  = {0};
     struct mx_mysql_bind result = {0};
     uint64_t job_id;
-    uint64_t *job_id_out;
+    uint64_t *job_id_out = NULL;
     int res;
 
    char *query =
@@ -321,7 +321,8 @@ uint64_t mxq_select_job_from_group(struct mx_mysql *mysql, uint64_t group_id)
     } else {
         job_id=0;
     }
-    free(job_id_out);
+    if (job_id_out)
+        free(job_id_out);
     return(job_id);
 }