(Desktop) Fix livebook stdout closed on non-utf8 bytes

[jonatanklosko]

Closes #3200.

The desktop app spawns the Livebook Elixir node and reads stdout. If an invalid UTF-8 byte appears in the stdout, the reader finishes and effectively closes the pipe for writing. Once the pipe is closed, trying to log to stdout crashes the :user process, causing the reported issue. Elixir/Erlang code should not produce a byte like this, however a NIF might print anything.

The error can be reproduced by writing invalid byte directly to stdout descriptor:

File.write("/dev/fd/1", <<0xFF>>)
require Logger
Logger.error("Hello")
Logger.error("Hello")

Once the stdout is closed, it is corrupted as long as the app is running. When a runtime is restarted, any logging triggers the same :user crash.

[wojtekmach]

Thank you!