res_pjsip_pubsub: Move where the subscription is stored to after initialized.

A problem arose when testing the AMI subscription listing actions where it
was possible for a subscription that had not been fully initialized to be
listed. This was problematic as the underlying listing code would crash.

This change makes it so the subscription tree is fully set up before it is
added to the list of subscriptions. This ensures that when the listing actions
get the subscription it is valid.

ASTERISK-25738 #close

Change-Id: Iace2b13641c31bbcc0d43a39f99aba1f340c0f48

res/res_pjsip_pubsub.c

@@ -1254,7 +1254,6 @@ static struct sip_subscription_tree *allocate_subscription_tree(struct ast_sip_e
 	sub_tree->endpoint = ao2_bump(endpoint);
 	sub_tree->notify_sched_id = -1;
 
-	add_subscription(sub_tree);
 	return sub_tree;
 }
 
@@ -1328,6 +1327,8 @@ static struct sip_subscription_tree *create_subscription_tree(const struct ast_s
 		sub_tree->is_list = 1;
 	}
 
+	add_subscription(sub_tree);
+
 	return sub_tree;
 }
 
@@ -1616,6 +1617,8 @@ struct ast_sip_subscription *ast_sip_create_subscription(const struct ast_sip_su
 		return NULL;
 	}
 
+	add_subscription(sub_tree);
+
 	return sub;
 }