add leaving status for leaving groups

Session/Home/HomeViewModel.swift

@@ -307,13 +307,19 @@ public class HomeViewModel {
                 case .closedGroup:
                     try MessageSender
                         .leave(db, groupPublicKey: threadId)
-                        .done { _ in
+                        .done { (interactionId, error) in
                             Storage.shared.writeAsync { db in
+                                if let _ = error {
+                                    try Interaction
+                                        .filter(id: interactionId)
+                                        .updateAll(db, Interaction.Columns.body.set(to: "group_leave_error".localized()))
+                                } else {
                                     _ = try SessionThread
                                         .filter(id: threadId)
                                         .deleteAll(db)
                                 }
                             }
+                        }
                         .retainUntilComplete()
                     
                 case .openGroup:

SessionMessagingKit/Sending & Receiving/Message Handling/MessageSender+ClosedGroups.swift

@@ -478,7 +478,7 @@ extension MessageSender {
     /// unregisters from push notifications.
     ///
     /// The returned promise is fulfilled when the `MEMBER_LEFT` message has been sent to the group.
-    public static func leave(_ db: Database, groupPublicKey: String) throws -> Promise<Int64> {
+    public static func leave(_ db: Database, groupPublicKey: String) throws -> Promise<(Int64, Error?)> {
         guard let thread: SessionThread = try? SessionThread.fetchOne(db, id: groupPublicKey) else {
             SNLog("Can't leave nonexistent closed group.")
             return Promise(error: MessageSenderError.noThread)
@@ -503,7 +503,9 @@ extension MessageSender {
         }
         
         // Send the update to the group
-        let promise = try MessageSender
+        let (promise, seal) = Promise<(Int64, Error?)>.pending()
+        do {
+            try MessageSender
                 .sendNonDurably(
                     db,
                     message: ClosedGroupControlMessage(
@@ -533,12 +535,15 @@ extension MessageSender {
                                 .infoMessage(db, sender: userPublicKey)
                         ).update(db)
                     }
-                
+                    seal.fulfill((interactionId, nil))
                 }
-            .map { _ in
-                return interactionId
+                .catch { error in
+                    seal.fulfill((interactionId, error))
+                }
+        }
+        catch {
+            seal.fulfill((interactionId, error))
         }
-            
         
         // Update the group (if the admin leaves the group is disbanded)
         let wasAdminUser: Bool = try GroupMember