This is a continuation of rB39f005eae8eed8b939579aff8c9a05a4f50e5e38
Now all the fields where we check for object type in RNA (like
rna_Curve_object_poll) will have a safe guard for when this isn't the
case. For example when loading files that has missing object libraries
and all missing objects are replaced with empties (placeholders).
Reviewed By: Brecht
Differential Revision: http://developer.blender.org/D5425