Fix empty value returned by FileRevealer::getSelectCommand() (#8281)

Changes `FileRevealer::getSelectCommand` to return an empty `QStringList` as a fallback, not an empty `std::optional`.

src/gui/FileRevealer.cpp

@@ -147,7 +147,7 @@ const QStringList& FileRevealer::getSelectCommand()
 	}
 
 	// Fallback to empty list
-	selectCommandCache = {};
+	selectCommandCache = QStringList{};
 	return selectCommandCache.value();
 }