The next client will remove the asserts. A future client will avoid trying to use files that don't exist.
The next client will ignore full paths for files that don't exist. It will also look in more places for non-pathed icons so it finds more than it used to.
Nothing extracted yet.
Steam was scanning my system for non-Steam games to add when it found a broken desktop file with an incorrect icon link, which it then tried to use to display in the dialog - hence asserts.