fix exception when receiving REFER but dial task ended (#1353)

lib/tasks/dial.js

@@ -777,6 +777,9 @@ class TaskDial extends Task {
         this.epOther.api('uuid_break', this.epOther.uuid);
         this.epOther.bridge(sd.ep);
       }
+      else {
+        this.logger.error('Dial:_connectSingleDial - no other endpoint to bridge!');
+      }
       this.bridged = true;
     }