send my public key to new members

lib/src/services/api/client2client/groups.c2c.dart

@@ -165,6 +165,9 @@ Future<bool> handleGroupJoin(
   if (await twonlyDB.contactsDao.getContactById(fromUserId) == null) {
     if (!await addNewHiddenContact(fromUserId)) {
       Log.error('Got group join, but could not load contact.');
+      // This can happen in case the group join was received before the group create.
+      // In this case return false, which will cause the receipt to fail and the user
+      // will resend this message.
       return false;
     }
   }

lib/src/services/group.services.dart

@@ -261,6 +261,20 @@ Future<(int, EncryptedGroupState)?> fetchGroupState(Group group) async {
           ),
         );
       }
+
+      // Send the new user my public group key
+      if (group.myGroupPrivateKey != null) {
+        final keyPair =
+            IdentityKeyPair.fromSerialized(group.myGroupPrivateKey!);
+        await sendCipherText(
+          memberId.toInt(),
+          EncryptedContent(
+            groupJoin: EncryptedContent_GroupJoin(
+              groupPublicKey: keyPair.getPublicKey().serialize(),
+            ),
+          ),
+        );
+      }
     }
 
     // check if there is a member which is not in the server list...