app_queue: Fix crash when using 'b' option on non-ringall queue.

When using the 'b' option to Queue with a queue that was not configured
for ring all a crash would occur as the wrong pointer would be used.

ASTERISK-28218

Change-Id: If1390f64e321047dff24fd2410c95dde74904980

apps/app_queue.c

@@ -4667,7 +4667,7 @@ static int ring_one(struct queue_ent *qe, struct callattempt *outgoing, int *bus
 			/* Ring just the best channel */
 			ast_debug(1, "Trying '%s' with metric %d\n", best->interface, best->metric);
 			ret = ring_entry(qe, best, busies);
-			if (qe->predial_callee && cur->chan) {
+			if (qe->predial_callee && best->chan) {
 				ast_autoservice_start(best->chan);
 			}
 		}