Fix directory and last commit not loading for some filenames

Filenames that contained special pathspec characters (see https://css-tricks.com/git-pathspecs-and-how-to-use-them) would not return a valid last commit or properly load in the repository browser. For example, :wq would cause the GraphQL endpoint to return a null lastCommit, and a file :wq/test.txt would not show the commit information in the repository browser.

This requires gitaly!2303 (merged) to work.