WIP: fix possible rare error-code 32 problem (seq too low)

Being hit by @Laiteux sometimes

Author: knocte

src/TgSharp.Core/Network/MtProtoSender.cs

@@ -38,9 +38,12 @@ public MtProtoSender(TcpTransport transport, ISessionStore sessionStore, Session
         private int GenerateSequence(bool confirmed)
         {
             lock (session.Lock) {
+                var lastSequence = session.Sequence;
+                var newSequence = lastSequence + 1;
                 try {
-                    return confirmed ? session.Sequence++ * 2 + 1 : session.Sequence * 2;
+                    return confirmed ? newSequence * 2 + 1 : newSequence * 2;
                 } finally {
+                    session.Sequence = newSequence;
                     sessionStore.Save(session);
                 }
             }