Ignore 'Broken Pipe' if child process does not read all of stdin

[arpankapoor]

Avoid the fuzzer from getting killed if the child process closes the other end of the pipe before the fuzzer has finished writing to it.
I'm not sure if this is an idiomatic way to do this or if this signal should be handled at the global level.

[domenukk]

Looks good thanks!
One thing, clippy suggets to remove one bracket:

error: this `else { if .. }` block can be collapsed
   --> libafl/src/executors/command.rs:142:24
    |
142 |                   } else {
    |  ________________________^
143 | |                     if let Err(err) = stdin.flush() {
144 | |                         if err.kind() != std::io::ErrorKind::BrokenPipe {
145 | |                             return Err(err.into());
146 | |                         }
147 | |                     }
148 | |                 }
    | |_________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_else_if
note: the lint level is defined here
   --> libafl/src/lib.rs:16:9
    |
16  | #![deny(clippy::all)]
    |         ^^^^^^^^^^^
    = note: `#[deny(clippy::collapsible_else_if)]` implied by `#[deny(clippy::all)]`
help: collapse nested if block
    |
142 ~                 } else if let Err(err) = stdin.flush() {
143 +                     if err.kind() != std::io::ErrorKind::BrokenPipe {
144 +                         return Err(err.into());
145 +                     }
146 +                 }
    |

[domenukk]

Thanks! :)