linux: Check for no desktop portal being present

[mihawk90]

Description

This adds an additional check to the existing checkWayland() to make sure we have an XDG Portal at all.

Motivation and Context

Came across a log in linux-support today, that looked like this:

Looks perfectly normal, right? Except, this user didn't have any XDG Portal set up at all, indicated by no [pipewire] prefixed line in the log. The existing [pipewire] No capture line is only logged when the Portal responds but is not giving us any capture methods.

I guess it could be argued this log line should also be output when there is no XDG portal at all, but I don't know if that's feasible and this works.

How Has This Been Tested?

With the aforementioned log.

Also tested three other logs to make sure it didn't break existing checks.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Tweak (non-breaking change to improve existing functionality)

Checklist:

• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[RytoEX]

Seems correct. @Penwy ?

[Penwy]

Small nit to improve efficience by not doing a full file search when we don't need to, otherwise LGTM.