Setup does not update existing installations in custom folder

If you choose a different folder to install LibreWolf into, an update will still try to install to the default folder. To fix this, for example the NSIS script could just check the default registry value in HKLM\SOFTWARE\Clients\StartMenuInternet\LibreWolf\shell\open\command and determine the correct installation path from it. If it can't, then the default path should be suggested.

(LibreWolf WinUpdater already makes sure the setup file doesn't reinstall in the default path, by using this registry value and NSIS's /D= switch.)

Edit: crap, apparently I misplaced this issue. Thanks @maltejur for moving it.