Qt: Use temporary game list entry for properties of playlists

Doesn't provide full functionality, but this is not a supported setup
and it's better than only making the first disc accessible.

src/core/fullscreenui_settings.cpp

@@ -1647,7 +1647,9 @@ bool FullscreenUI::SwitchToGameSettingsForPath(const std::string& path, Settings
 {
   auto lock = GameList::GetLock();
   const GameList::Entry* entry = !path.empty() ? GameList::GetEntryForPath(path) : nullptr;
-  if (!entry || entry->serial.empty())
+
+  // playlists will always contain the first disc's serial, so use the current game instead
+  if (!entry || entry->serial.empty() || entry->type == GameList::EntryType::Playlist)
   {
     Host::RunOnCoreThread([page]() {
       Error error;

src/duckstation-qt/mainwindow.cpp

@@ -2782,7 +2782,9 @@ void MainWindow::openGamePropertiesForCurrentGame(const char* category /* = null
     // show for first disc instead
     entry = GameList::GetFirstDiscSetMember(entry->dbentry->disc_set);
   }
-  if (entry)
+
+  // playlists will always contain the first disc's serial, so use the current game instead
+  if (entry && entry->type != GameList::EntryType::Playlist)
     SettingsWindow::openGamePropertiesDialog(entry, category);
   else
     g_core_thread->openGamePropertiesForCurrentGame(category ? QString::fromUtf8(category) : QString());