Add missing boundary at end of multipart/form-data request body for requests that include no application/octet-stream data

This makes the sync request sent to the /download endpoint valid multipart/form-data according to RFC 2046, 5.1

anki/sync.py

@@ -582,7 +582,7 @@ Content-Type: application/octet-stream\r\n\r\n""")
                         tgt.close()
                     break
                 tgt.write(data)
-            buf.write(b'\r\n' + bdry + b'--\r\n')
+        buf.write(b'\r\n' + bdry + b'--\r\n')
         size = buf.tell()
         # connection headers
         headers = {