Handle write errors for LSP connections in Vim

For various reasons, calls to `ch_sendraw` can fail with the following error.

```
E631: ch_sendraw(): write failed
```

We should wrap every call in a `try ... catch` block, and handle these errors. We should probably log an error message in `:ALEInfo`, or ignore the error entirely. Preferably the former. We cannot prevent the errors from happening. See #1994.