Assistant: Fix index updating on startup in the remote control mode

HelpEngineWrapper::initialDocSetupDone() should be called only once
right after the initialization of the help models. Calling it on
every small update leads to recursion.

Task-number: QTBUG-36850
Change-Id: I16cae03f08bbc9a19ec9298c84c602a4046dce93
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>