Build icon for commit view goes to 'undefined'

Issue Summary

When viewing a single commit (not in a PR), if you hover over the build icon (not the text, just the icon) for a legacy build (builds posted to BbS prior to version 7.4), the link ends with undefined and leads to a 404 page:

Bitbucket_URL/projects/PROJECT_NAME/repos/REPO_NAME/undefined

Steps to Reproduce

1. Click on the commit view list
2. Find a commit with builds posted to BbS prior to being on version 7.4 (find an old commit)
3. Click on the builds icon

Expected Results

User is navigated to the correct build on the builds tab

Actual Results

User is navigated to a 404 page: 

Bitbucket_URL/projects/PROJECT_NAME/repos/REPO_NAME/undefined

Workaround

• Upgrade to 7.6 or above (we plan on back-porting this fix to 7.4 and 7.5)
• Navigate to the builds tab directly and find the build using the selector