fix erroneous error-handling in frame filter code

fix erroneous error-handling in frame filter code

This fixes PR python/16487.

The bug here is that the function-name-handling code in py_print_frame
had a small logic error (really a misplaced closing brace).  This
error could lead to a Py_DECREF(NULL), which crashes.

This patch fixes the bug in the obvious way.

Built and regtested on x86-64 Fedora 18.  New test case included.

2014-01-23  Tom Tromey  <tromey@redhat.com>

	PR python/16487:
	* python/py-framefilter.c (py_print_frame): Don't call Py_DECREF
	on a NULL pointer.  Move "goto error" to correct place.

2014-01-23  Tom Tromey  <tromey@redhat.com>

	PR python/16487:
	* gdb.python/py-framefilter.exp: Add test using "Error" filter.
	* gdb.python/py-framefilter.py (ErrorInName, ErrorFilter): New
	classes.