Fix SF #633935, test_bz2 fails

Needed to init ret since it was Py_XDECREF()d on error.
All regressions pass in debug build for me.

Modules/bz2module.c

@@ -1701,7 +1701,7 @@ BZ2Decomp_decompress(BZ2DecompObject *self, PyObject *args)
 	int datasize;
 	int bufsize = SMALLCHUNK;
 	long totalout;
-	PyObject *ret;
+	PyObject *ret = NULL;
 	bz_stream *bzs = &self->bzs;
 	int bzerror;