Skip ES commit results for deleted projects

What does this MR do?

Ref: https://gitlab.com/gitlab-org/gitlab-ee/issues/12578

Attempting to render commit results for deleted projects raised a NoMethodError and resulted in a 500 error.

This can happen between the time a project deletion is triggered and the ProjectDestroyWorker has run in a background job.

This fixes the immediate error, if I find any problems with the ES deletion callbacks not being triggered correctly I'll submit that in another MR.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [-] Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team