D14158: Avoid a kio-mtp crash when trying to add a blocked device to the device cache

[Elvis Angelaccio]

elvisangelaccio accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R320 KIO Extras

REVISION DETAIL
  https://phabricator.kde.org/D14158

To: jtamate, #frameworks, elvisangelaccio
Cc: broulik