Fix empty ifs causing errors on spirv 1.6

[Vecvec]

Connections
Fixes #7882

Description
Skips if statements if both the accept and reject blocks are empty, they don't do anything so we can just not write them out.

Testing
Adds a snapshot test.

Squash or Rebase?
Squash.

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests.
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.