pmv panicks when the source was the root directory

[sgryjp]

Summary

pmv panicks when the source was the root directory.

Expected behavior

pmv try to move the root directory, instead of panicking.

Version

0.4.1

Steps to reproduce

1. Execute pmv / .

Example output

$ pmv -n / .
thread 'main' panicked at 'assertion failed: !patterns.is_empty()', /Users/sgryjp/.cargo/.../pmv-0.4.1/src/walk.rs:44:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace