Fix PTY performance regressions

The patch 9e7655e introduced some changes which improved rendering with
very dense grids, but the automatic benchmarks indicated a slight
performance difference in the `dense_cells` benchmark.

Caching the terminal lock between iterations rather than always calling
`try_lock` resolves that issue.

While breaking early in the `WouldBlock` case with `unprocessed != 0`
does also help resolve these issues, it shows some more significant
fluctuations. Combining both fixes does not help.

Additionally on Windows receiving `Ok(0)` from the PTY will also occur
instead of a `WouldBlock` error, so handling that fixes freezing on
Windows.

Fixes #5305.

0 files changed, 0 insertions, 0 deletions