If an invalid filter type is supplied, don't run the queries.
This showed up with GPS dialog, since the PUI combo box defaults to
no entry selected, not the first entry.
This allows Nasal code attached to scenery models access their
world position and orientation by calling _model.getPose().
Also ensure models are attached to the scenegraph before Nasal
load scripts are called. This ensures that the world position
and orientation are available upon executing the load script.
Ensure all FGPositioned related functions return SGSharedPtr
instead of raw pointers to allow automatic conversion to
nasal ghosts without custom helper functions.
For now it is available in the positioned Nasal
module. FGAirport is fully ported, but especially
procedures/navaids and free functions are still
missing.
