cli: add Invalid mode

Silences compile warning

src/cli.h

@@ -13,6 +13,7 @@ class CLI : public QObject
 
 public:
     enum Mode {
+        Invalid,
         ExportContacts,
         ExportTxHistory,
         BruteforcePassword

src/main.cpp

@@ -176,6 +176,7 @@ if (AttachConsole(ATTACH_PARENT_PROCESS)) {
                 return CLI::Mode::ExportTxHistory;
             if (bruteforcePassword)
                 return CLI::Mode::BruteforcePassword;
+            return CLI::Mode::Invalid;
         }();
 
         CLI cli{mode, &parser, &app};