Mask reserved bit when parsing GoAway and WindowUpdate frames by bysiber · Pull Request #168 · python-hyper/hyperframe

GoAwayFrame.serialize_body already masks last_stream_id with
& 0x7FFFFFFF, but parse_body reads the raw 32-bit value without
stripping the reserved top bit. If a peer happens to set that bit,
last_stream_id would be read as a value >= 2^31 instead of the
actual stream ID.

Similarly, WindowUpdateFrame.serialize_body masks window_increment
with & 0x7FFFFFFF, but parse_body doesn't. If the reserved bit is
set, the unmasked value exceeds 2^31-1 and the frame is rejected
with InvalidDataError — even though RFC 9113 Section 6.9 says the
reserved bit "MUST be ignored when receiving."

The rest of the codebase already follows this pattern:
  - Frame.parse_frame_header masks stream_id & 0x7FFFFFFF
  - Priority.parse_priority_data masks depends_on & 0x7FFFFFFF

Add the same mask to GoAwayFrame.parse_body and
WindowUpdateFrame.parse_body for consistency.