Manage the case someone is asking for the attached of an applet

Even if is api is not supposed to be used as doesn't make sense,
is techincally possible, for instance in containments code,
to ask for the Plasmoid attached property of an item which is an pplaet
itself, which used to crash.
Now handle specificly that case by returning itself. it's a kinda
useless api in that context but is way better than crashing