Plasma 5.7 introduced some changes that exposed a bug in Ark, resulting in the
app not starting when invoked from the start menu or KRunner.

Dropping the X-KDE-HasTempFileOption property from the Ark .desktop file fixes
this issue.

This property was (wrongly) set in commit bc6dcce5, where Ark was ported
away from KUniqueApplication.

Thanks to Ragnar Thomsen for the bugfix.