Check whether the VolumeSnapshot's source PVC is nil before using it

[blackpiglet]

Thank you for contributing to Velero!

Please add a summary of your change

Two changes are involved in this PR:

• Check whether the VolumeSnapshot's source PVC is nil before using it.
• Skip populate VolumeInfo for data-moved PV when CSI is not enabled.

Does your change fix a particular issue?

Fixes #7494

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 61.62%. Comparing base (79e9e31) to head (f8deea1).

Files	Patch %	Lines
internal/volume/volumes_information.go	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7515      +/-   ##
==========================================
- Coverage   61.62%   61.62%   -0.01%     
==========================================
  Files         263      263              
  Lines       28681    28688       +7     
==========================================
+ Hits        17675    17678       +3     
- Misses       9758     9761       +3     
- Partials     1248     1249       +1     

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

[pavlospt]

@blackpiglet can we please cherry-pick it to release-1.12.5?