See technique used in `fast-syntax-highlighting`:
- ca2e18bbc9
- http://www.zsh.org/mla/users/2018/msg00424.html
Also see http://www.zsh.org/mla/users/2018/msg00432.html
In async response handler:
- We only want to read data in case of POLLIN or POLLHUP. Not POLLNVAL
or select error.
- We always want to remove the handler, so it doesn't get called in an
infinite loop when error is nval or err.
There is an upstream bug that prevents ctrl-c from resetting the prompt
immediately after a suggestion has been fetched asynchronously. A patch
has been submitted, but a workaround for now is to add `command true`
after the exec.
See https://github.com/zsh-users/zsh-autosuggestions/issues/364
