Don't crash when receiving SASL lines from server without having negotiated SASL via CAP

Reported by Noisytoot on Pissnet, thanks

modules/sasl.cpp

@@ -196,6 +196,7 @@ class CSASLMod : public CModule {
     }
 
     void Authenticate(const CString& sLine) {
+        if (m_Mechanisms.empty()) return;
         /* Send blank authenticate for other mechanisms (like EXTERNAL). */
         CString sAuthLine;
         if (m_Mechanisms.GetCurrent().Equals("PLAIN") && sLine.Equals("+")) {
@@ -249,6 +250,7 @@ class CSASLMod : public CModule {
     }
 
     EModRet OnNumericMessage(CNumericMessage& msg) override {
+        if (m_Mechanisms.empty()) return CONTINUE;
         if (msg.GetCode() == 903) {
             /* SASL success! */
             if (m_bVerbose) {

test/integration/tests/modules.cpp

@@ -268,5 +268,17 @@ INSTANTIATE_TEST_CASE_P(SaslInst, SaslModuleTest,
                                 99,
                                 {SaslModuleTest::Prefix() + "YmJi", "Yg=="}}));
 
+TEST_F(ZNCTest, SaslMechsNotInit) {
+    auto znc = Run();
+    auto ircd = ConnectIRCd();
+    auto client = LoginClient();
+    client.Write("znc loadmod sasl");
+    client.Write("PRIVMSG *sasl :set * *");
+    client.ReadUntil("Password has been set");
+    ircd.Write("AUTHENTICATE +");
+    ircd.Write("PING foo");
+    ircd.ReadUntil("PONG foo");
+}
+
 }  // namespace
 }  // namespace znc_inttest