Freeze happened when reloading a library while having an Object property
with a custom getter function defined in Python.
Just piggybacking on rB62eb21e3ce87, this just applies the same fix (use
the BPy_BEGIN/END_ALLOW_THREADS macros) to the places where the freeze
happens in the report situation.
All credit goes to @Brecht Van Lommel (brecht) and @Bastien Montagne (mont29).