qcacmn: Fix possible null pointer dereference

Fix possible null pointer dereference glagged by static analysis

Change-Id: I100619888318182c19300bcbbcd95e9c68efe8a5
CRs-Fixed: 2417910

umac/scan/core/src/wlan_scan_manager.c

@@ -149,6 +149,8 @@ static void scm_scan_post_event(struct wlan_objmgr_vdev *vdev,
 	}
 	scan = wlan_vdev_get_scan_obj(vdev);
 	pdev_ev_handler = wlan_vdev_get_pdev_scan_ev_handlers(vdev);
+	if (!pdev_ev_handler)
+		return;
 	cb_handlers = &(pdev_ev_handler->cb_handlers[0]);
 	requesters = scan->requesters;