DisplaySettings: Allow setting wallpapers from outside /res/wallpapers

Ideally, we would copy the file to `/res/wallpapers`, add an entry to
`ComboBox` model and set the index to this entry. I didn't want to
touch anything outside of `DisplaySettings`, so this is more of a
workaround :^)

Applications/DisplaySettings/DisplaySettings.cpp

@@ -125,6 +125,11 @@ void DisplaySettingsWidget::create_frame()
  m_wallpaper_combo->set_model(*ItemListModel<AK::String>::create(m_wallpapers));
  m_wallpaper_combo->on_change = [this](auto& text, const GUI::ModelIndex& index) {
  String path = text;
+ if (m_monitor_widget->set_wallpaper(path)) {
+ m_monitor_widget->update();
+ return;
+ }
+
  if (index.row() == 0) {
  path = "";
  } else {
@@ -136,8 +141,8 @@ void DisplaySettingsWidget::create_frame()
  }
  }
 
- this->m_monitor_widget->set_wallpaper(path);
- this->m_monitor_widget->update();
+ m_monitor_widget->set_wallpaper(path);
+ m_monitor_widget->update();
  };
 
  auto& button = wallpaper_selection_container.add<GUI::Button>();

Applications/DisplaySettings/MonitorWidget.cpp

@@ -33,10 +33,14 @@ MonitorWidget::MonitorWidget()
  m_monitor_rect = { 8, 9, 320, 180 };
 }
 
-void MonitorWidget::set_wallpaper(String path)
+bool MonitorWidget::set_wallpaper(String path)
 {
  m_desktop_wallpaper_path = path;
- m_desktop_wallpaper_bitmap = Gfx::Bitmap::load_from_file(path);
+ auto bitmap_ptr = Gfx::Bitmap::load_from_file(path);
+ if (!bitmap_ptr)
+ return false;
+ m_desktop_wallpaper_bitmap = bitmap_ptr;
+ return true;
 }
 
 String MonitorWidget::wallpaper()

Applications/DisplaySettings/MonitorWidget.h

@@ -35,7 +35,7 @@ class MonitorWidget final : public GUI::Widget {
 public:
  MonitorWidget();
 
- void set_wallpaper(String path);
+ bool set_wallpaper(String path);
  String wallpaper();
 
  void set_wallpaper_mode(String mode);