bpo-31848: Fix broken error handling in Aifc_read.initfp() when the SSND chunk is not found (GH-5240)


Initialize self._ssnd_chunk so that aifc.Error is raised as intended,
not AttributeError.
(cherry picked from commit 80d20b918bd8a882043c493a7f958333ecb41727)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>
4 files changed