fix(rpc): redraw parse failure silently closes channel #42220

Problem:
When `unpacker_parse_redraw()` fails, it closes the unpacker without
setting `unpack_error`, so `chan_close_on_err()` gets a NULL message.
A pending request fails with an empty error (`RPC: (null)`).

c04d0734a728 fixed the crash that followed (advancing the closed
unpacker), but not the silent close itself.

Repro:
Self-attach (`nvim_ui_attach` on a loopback `sockconnect()` channel)
closes the channel without a visible reason, either while
`nvim_ui_attach` is pending or at the next redraw.

Solution:
Set an error msg when `unpacker_parse_redraw()` fails.

Note:
Self-attach fails for accidental reasons, not by design:
- An incoming "redraw" notif is always parsed "as a UI client"
  (`handle_ui_client_redraw`), whose `grid_line` buffer is only
  allocated in a UI client process. A loopback channel is both ends, so
  it parses its own redraw stream as if it were the TUI.
- Even if parsing worked, `parse_msgpack()` drops redraw events unless
  `ui_client_attached`, and a `sockconnect()` client has no notification
  callback.

0 files changed, 0 insertions, 0 deletions