reintegrate commented assert

this assert did not work when saving with asynctask - list was not updated.
now it's possible to disable async saving, which is done at the top of this testmethod.

jenkins run of testclass: https://jenkins.catrob.at/job/Catroid-single-UI-emulator/304/
failing test is annotated with '@'Device and can be ignored in Emulatorrun.

jenkins run of single test: https://jenkins.catrob.at/job/Catroid-single-UI-emulator/305/console

after this is merged, issue #646 can be closed!