gs-application: Search for the installed application in app.launch
To reproduce:
- Search for an Flatpak app that you haven't installed
- Click "Install"
- View a different window, or go to a different workspace
- Wait to get the "X is now installed" notification
- Hover the mouse over it to see the "Launch" button, and click it
Expected results: the installed app will launch.
Actual results: nothing happens.
Following the same steps for a package-based app launches it.