py_decref: Don't check for NULL before calling Py_DECREF.

py_decref: Don't check for NULL before calling Py_DECREF.

The only difference between Py_DECREF and Py_XDECREF is that the latter allows passing
in a NULL object, while the former prohibits it.  Given that, it's natural to expect
the same from py_decref vs py_xdecref.

gdb/
2013-05-21  Pedro Alves  <palves@redhat.com>

	* python/py-prettyprint.c (apply_val_pretty_printer): Check
	whether PRINTER is NULL before installing a Py_DECREF cleanup.
	* python/py-utils.c (py_decref): Don't check for NULL before
	calling Py_DECREF.