dispatcher: release lock instead of destroy when cleaning active calls hash table

- this could happen when dispatcher list was reloaded
- reported and fix by Dmitry, closes FS#275

modules/dispatcher/ds_ht.c

@@ -170,7 +170,7 @@ int ds_ht_clear_slots(ds_ht_t *dsht)
 		}
 		dsht->entries[i].first = NULL;
 		dsht->entries[i].esize = 0;
-		lock_destroy(&dsht->entries[i].lock);
+		lock_release(&dsht->entries[i].lock);
 	}
 	return 0;
 }