bindings/python: Handle import failures without crashing

bindings/python: Handle import failures without crashing

When the import of gi.repository.GLib failed, we would get a NULL
pointer that we passed along without any checking. In this situation,
the entire program would crash with a segmentation fault, and no
message to indicate the problem.

When the import fails, abort the SWIG init and print a message. The
Python interpreter then prints out a backtrace, which can be useful
in tracking down the problem.