Get file status for a single file.
This is not quite the same as calling git_status_foreach_ext()
with
the pathspec set to the specified path.
The status value for the file
The file to retrieve status for, rooted at the repo's workdir
0 on success, GIT_ENOTFOUND if the file is not found in the HEAD, index, and work tree, GIT_EINVALIDPATH if path
points at a folder, GIT_EAMBIGUOUS if "path" matches multiple files, -1 on other error.