user statistics: Hide approvals if 0

[ErikHumphrey]

If a user both has made no approvals, user profiles shouldn't show "Approvals: 0" in the stats table for the user or other users.

Almost all users are never approvers, so there's no point in showing this stat, but it should show if they made approvals when they were an approver in the past.

Optionally, it could also still show if the user is an approver, but "approver with 0 approvals" is a rare case, so maybe a second condition isn't worth implementing.