Avoid potentially sending message to deallocated instance

The m_pFilterControl is always added to the m_aActiveControls list
(see createFilterControl()), so it has been released by the loop over
the list. So make sure to call setTarget before the loop.

For some reason this doesn't normally cause sending a message to a
deallocated instance, though. (I only noticed it when experimenting
with if-zeroing out the creation of the user pane.) I guess this might
mean that we actually have a leak here, if the controls in the list
don't actually get deallocated by the release messages in the loop?

Change-Id: If691f8d35bab606ce8a61f677d8e495e72a23148