It shouldn't be possible to open second main window
By clicking "New Window" in dash context menu, or simply by running Games the second time in terminal, it's possible to have more than 1 main window open at the same time:
Needless to say, this badly breaks collection and shouldn't be possible.
It needs a check in
src/ui/application.vala to just bring the existing window in focus (we already have such a check for preferences window), and desktop file should be changed not to include "New Window".