Fix all warnings from the cppcoreguidelines-pro-type-member-init clang-tidy check (#4426)

src/controllers/commands/Command.hpp

@@ -10,7 +10,7 @@ namespace chatterino {
 struct Command {
     QString name;
     QString func;
-    bool showInMsgContextMenu;
+    bool showInMsgContextMenu{};
 
     Command() = default;
     explicit Command(const QString &text);