ensure error in else is forwarded appropriately

[merelymyself]

Description

Fixes #7407.

/home/gabriel/CodingProjects/nushell〉if false { 'a' } else { $foo }    12/09/2022 08:14:48 PM
Error: nu::parser::variable_not_found (link)

  × Variable not found.
   ╭─[entry #1:1:1]
 1 │ if false { 'a' } else { $foo }
   ·                         ──┬─
   ·                           ╰── variable not found
   ╰────

User-Facing Changes

(List of all changes that impact the user experience here. This helps us keep track of breaking changes.)

Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

• cargo fmt --all -- --check to check standard code formatting (cargo fmt --all applies these changes)
• cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect to check that you're using the standard code style
• cargo test --workspace to check that all tests pass

After Submitting

If your PR had any user-facing changes, update the documentation after the PR is merged, if necessary. This will help us keep the docs up to date.

[sholderbach]

I am no parser internals expert, but this looks good to me. Errors remain errors and the tests covers the motivating issue.

[kubouch]

Perfect, thanks!

[rgwood]

Nice one.