[stable7] fixes undefined appitem - fixes #12396

cc @ppaysant @DeepDiver1975 @jancborchardt 

This simply removes the entry in the navigation menu. Nothing big and persistent just UX (better than an error). Another solution would be to simply drop that line. Opinions?

@karlitschek @craigpg Please approve this fix in stable7

No need to forward port this to master as this is a stable7 only problem.
@PVince81 @LukasReschke there was a special js function to be used for such cases - right?