When using narrow, we get entries from ctx.walk() that aren't files, they're the
roots of ignored/excluded trees. These paths end with a /, so just skip them
when doing the walk.
Example narrowspec:
[include] path:foo/bar [exclude]
Example repo:
foo/bar/file1.txt foo/baz/file2.txt
When walking, we'll see:
foo/bar/file1.txt foo/baz/