CLI-1435: PHP error - undefined array key handled in pull command

[rahulgupta-acquia]

Motivation

Fixes CLI-1435

Proposed changes

Alternatives considered

Testing steps

1. Follow the contribution guide to set up your development environment or download a pre-built acli.phar for this PR.
2. If running from source, clear the kernel cache to pick up new and changed commands: ./bin/acli ckc
3. Run pull:files and select an ACSF environment with no sites deployed
4. Observe that the command exits gracefully instead of throwing an undefined array error.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.92%. Comparing base (304cc82) to head (81d261d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1844   +/-   ##
=========================================
  Coverage     92.92%   92.92%           
- Complexity     1846     1847    +1     
=========================================
  Files           123      123           
  Lines          6964     6966    +2     
=========================================
+ Hits           6471     6473    +2     
  Misses          493      493           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[github-actions]

Try the dev build for this PR: https://acquia-cli.s3.amazonaws.com/build/pr/1844/acli.phar

curl -OL https://acquia-cli.s3.amazonaws.com/build/pr/1844/acli.phar
chmod +x acli.phar

[danepowell]

You'll need to add a test case to cover this line. I'd suggest copying testRefreshAcsfFiles from PullFilesCommandTest.php and modify it to expect this exception. You'll need to modify mockGetAcsfSites() to return 0 sites to trigger the exception.