Ignore SendErrors when handling grammars

[Frojdholm]

When handling grammars, fetching and building is done in a thread pool. Results are communicated over channels and the receiving channel is closed on first error. This causes subsequent sends to fail causing a mess in stderr. This ignores all SendErrors causing only the first error to be printed.

Solves #2642

[the-mikedavis]

Before:

thread 'thread 'thread '<unnamed><unnamed>' panicked at '' panicked at 'thread 'called `Result::unwrap()` on an `Err` value: SendError { .. }called `Result::unwrap()` on an `Err` value: SendError { .. }', ', helix-loader/src/grammar.rshelix-loader/src/grammar.rs::136136::3535<unnamed>
' panicked at 'called `Result::unwrap()` on an `Err` value: SendError { .. }', helix-loader/src/grammar.rs
thread 'thread '<unnamed><unnamed><unnamed>' panicked at '' panicked at '' panicked at 'called `Result::unwrap()` on an `Err` value: SendError { .. }called `Result::unwrap()` on an `Err` value: SendError { .. }', ', helix-loader/src/grammar.rs::136:136called `Result::unwrap()` on an `Err` value: SendError { .. }35', 
helix-loader/src/grammar.rs:136:35
:thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: SendError { .. }', helix-loader/src/grammar.rs:35136
:35
helix-loader/src/grammar.rs:136:35
thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: SendError { .. }', helix-loader/src/grammar.rs:136:35
stack backtrace:
Error: Failed to fetch some grammar(s)

Caused by:
    0: Could not create grammar directory "/home/michael/dev-tools/code/helix/rttest/grammars/sources/rust"
    1: Permission denied (os error 13)

After:

Error: Failed to fetch some grammar(s)

Caused by:
    0: Could not create grammar directory "/home/michael/dev-tools/code/helix/rttest/grammars/sources/rust"
    1: Permission denied (os error 13)

Nice, this really cleans it up 👍