Scanning QR code makes an exception pop up (but things continue to work)

[hpk42]

When i use master Desktop and go to qr-code scanning i get an exception but on second attempt it works.
Not sure it needs to be considered a blocker, also good if someone else could verify this problem on a properly installed ".deb" package or so. I am using master core/desktop from github.

[Simon-Laux]

this was introduced by #3252, looks like the function in question systemPreferences.askForMediaAccess is not defined in non-mac builds.

#3278 attempts to fix it, if that shouldn't work then we can also remove those platform permission functions again, it already worked before them, so I don't think they actually did anything useful...