Fix division by zero for blame age map

Merged Jeff Stubler requested to merge brunsa2/gitlab-ce:35441-fix-division-by-zero into master

What does this MR do?

Fixes a division by zero error when the project is less than 1 day old.

Are there points in the code the reviewer needs to double check?


Why was this MR needed?

Viewing blame page on project less than 1 day old results in error.

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #35441 (closed)

Edited by Jeff Stubler