[2.7] bpo-31848: Fix broken error handling in Aifc_read.initfp() when the SSND chunk is not found (GH-5240) (GH-5781)

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>
diff --git a/Lib/aifc.py b/Lib/aifc.py
index e678327..981f801 100644
--- a/Lib/aifc.py
+++ b/Lib/aifc.py
@@ -308,6 +308,7 @@
         else:
             raise Error, 'not an AIFF or AIFF-C file'
         self._comm_chunk_read = 0
+        self._ssnd_chunk = None
         while 1:
             self._ssnd_seek_needed = 1
             try:
diff --git a/Lib/test/test_aifc.py b/Lib/test/test_aifc.py
index d1b7dd0..92bbe7b 100644
--- a/Lib/test/test_aifc.py
+++ b/Lib/test/test_aifc.py
@@ -214,6 +214,14 @@
         b = io.BytesIO('FORM' + struct.pack('>L', 4) + 'AIFF')
         self.assertRaises(aifc.Error, aifc.open, b)
 
+    def test_read_no_ssnd_chunk(self):
+        b = b'FORM' + struct.pack('>L', 4) + b'AIFC'
+        b += b'COMM' + struct.pack('>LhlhhLL', 38, 0, 0, 0, 0, 0, 0)
+        b += b'NONE' + struct.pack('B', 14) + b'not compressed' + b'\x00'
+        with self.assertRaisesRegexp(aifc.Error, 'COMM chunk and/or SSND chunk'
+                                                 ' missing'):
+            aifc.open(io.BytesIO(b))
+
     def test_read_wrong_compression_type(self):
         b = 'FORM' + struct.pack('>L', 4) + 'AIFC'
         b += 'COMM' + struct.pack('>LhlhhLL', 23, 0, 0, 0, 0, 0, 0)