Legitimate zero-length reads could cause spurious unexpected EOF,
since we implicitly assumed buffers always have remaining capacity.
For the buffered case, `consume(0)` could cause panics after either
`poll_fill_buf` or `poll_read` had returned `Poll::Pending`.
The bytes_read/with_limited logic receives a stylistic cleanup to make
it obvious that bytes_read is always written before being used.
Change-Id: I46aa47113309552dcef9532b5d4009d2186db9cd
Reviewed-on: https://cl.snix.dev/c/snix/+/30492
Tested-by: besadii
Reviewed-by: Brian Olsen <brian@maven-group.org>
Reviewed-by: Florian Klink <flokli@flokli.de>
83c3305863