Stop ZNC from prepending '#' if missing in join command.

Fixes #1794

src/Client.cpp

@@ -375,7 +375,7 @@ void CClient::AuthUser() {
     }
 }
 
-/** Username+password auth, which reports success/failure to client via SASL. */ 
+/** Username+password auth, which reports success/failure to client via SASL. */
 class CClientSASLAuth : public CClientAuth {
   public:
     using CClientAuth::CClientAuth;
@@ -1463,7 +1463,7 @@ bool CClient::OnJoinMessage(CJoinMessage& Message) {
                 else
                     pChan->JoinUser(sKey);
                 continue;
-            } else if (!sChannel.empty()) {
+            } else if (!sChannel.empty() && m_pNetwork->IsChan(sChannel)) {
                 pChan = new CChan(sChannel, m_pNetwork, false);
                 if (m_pNetwork->AddChan(pChan)) {
                     pChan->SetKey(sKey);

test/integration/tests/core.cpp

@@ -1463,5 +1463,28 @@ TEST_F(ZNCTest, MotdBufferDoesNotAccumulate376) {
                 Not(HasSubstr("End of /MOTD command")));
 }
 
+// https://github.com/znc/znc/issues/1794
+TEST_F(ZNCTest, PrependJoinBug) {
+    auto znc = Run();
+    auto ircd = ConnectIRCd();
+    auto client = LoginClient();
+
+    ircd.Write(":server 001 nick :Hello");
+    ircd.Write(":server 005 nick CHANTYPES=# :supports");
+    client.ReadUntil("005");
+
+    client.Write("JOIN 0");
+    ircd.ReadUntil("JOIN 0");
+
+    client.Write("znc listchans");
+    ASSERT_THAT(client.ReadRemainder().toStdString(), Not(HasSubstr("#0")));
+
+    client.Write("JOIN test");
+    ircd.ReadUntil("JOIN test");
+
+    client.Write("znc listchans");
+    ASSERT_THAT(client.ReadRemainder().toStdString(), Not(HasSubstr("#test")));
+}
+
 }  // namespace
 }  // namespace znc_inttest