Don't fail the entire repository overview page if identifying the license fails

Gitaly's FindLicense was recently ported to Go from Ruby. This introduced some disparities as Gitaly now provides more license short names than Rails handles. When Rails receives a license it doesn't handle, the whole repository overview page fails to render. This was identified in a production incident. Instead of failing to render the entire page, we should fallback to showing just License instead of the short name as described in #12914 (comment 669535259).