Only validate encryption key, if it is actually set (fixes d49a5d6f)

Source commit: 8a909d9d6a2c0f31ad2128bdc59661a0e7cd5df9

source/core/Terminal.cpp

@@ -1142,7 +1142,10 @@ void __fastcall TTerminal::Open()
   try
   {
     FEncryptKey = HexToBytes(FSessionData->EncryptKey);
-    ValidateEncryptKey(FEncryptKey);
+    if (IsEncryptingFiles())
+    {
+      ValidateEncryptKey(FEncryptKey);
+    }
 
     DoInformation(L"", true, 1);
     try