LibGUI: Show an error message on open error in the FilePicker

Author: https://github.com/krkk
Commit: 80e3cf3ef7
Pull-request: https://github.com/SerenityOS/serenity/pull/9037
Reviewed-by: https://github.com/gunnarbeutner ✅

Userland/Libraries/LibGUI/FilePicker.h

@@ -68,6 +68,8 @@ private:
     NonnullRefPtr<FileSystemModel> m_model;
     String m_selected_file;
 
+    RefPtr<GUI::Label> m_error_label;
+
     RefPtr<TextBox> m_filename_textbox;
     RefPtr<TextBox> m_location_textbox;
     Vector<CommonLocationButton> m_common_location_buttons;