closes#2843
Previously, bad partial matches between cwd and target buffer path would
result in non-cwd buffers showing up in the picker despite using
`only_cwd=true`.
eg.
cwd = `/foo/bar`
target buffer = `foo/bar1/baz.txt`
The target buffer starts with the cwd path.
This is fixed by appending a path separator before comparing/matching:
eg.
cwd = `/foo/bar/`
target buffer = `foo/bar1/baz.txt`