formula_installer: handle nil runtime dependencies

[EricFromCanada]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

Some old bottles (Sierra and earlier) will fail to install when the downloaded bottle manifest has its runtime_dependencies set to null rather than []. This happens during manifest generation when Tab finds the tab's homebrew_version to be either not present or earlier than 1.1.6. The existing fetch_bottle_tab method passes an empty list if runtime_dependencies is not present; this change ensures that the same happens if runtime_dependencies is present but nil.

Also, Tab#runtime_dependencies could return an empty list if homebrew_version < 1.1.6 to avoid this in future manifests. Not sure if that's necessary.

Before:

==> Downloading https://ghcr.io/v2/homebrew/core/libcuefile/manifests/r475-1
Already downloaded: /Users/vmadmin/Library/Caches/Homebrew/downloads/bcfd5f9c5e66525827bd2c1024f9dbee05db47868b3077b3e19178fe9e25fd91--libcuefile-r475-1.bottle_manifest.json
Error: undefined method `each_with_object' for nil:NilClass

After:

==> Downloading https://ghcr.io/v2/homebrew/core/libcuefile/manifests/r475-1
Already downloaded: /Users/vmadmin/Library/Caches/Homebrew/downloads/bcfd5f9c5e66525827bd2c1024f9dbee05db47868b3077b3e19178fe9e25fd91--libcuefile-r475-1.bottle_manifest.json
==> Fetching libcuefile
==> Downloading https://ghcr.io/v2/homebrew/core/libcuefile/blobs/sha256:66ec2d9281a5459326a1b2d220b9f68fa241a6b9f8370324377af
Already downloaded: /Users/vmadmin/Library/Caches/Homebrew/downloads/f1ebb348b1ce9b4e5bd593221f88ed9bd76af0441b08cf3acda6e7fe1c45306e--libcuefile--r475.sierra.bottle.1.tar.gz
==> Pouring libcuefile--r475.sierra.bottle.1.tar.gz
🍺  /usr/local/Cellar/libcuefile/r475: 11 files, 177.2KB
==> Running `brew cleanup libcuefile`...

[Bo98]

Thanks!

[MikeMcQuaid]

Makes sense, thanks @EricFromCanada!