Renaming a file unexpectedly places it outside of pre-opened directory

[nr6000000]

Describe the bug

Whenever a file is renamed it's placed outside of pre-opened directory. It happens only if the file isn't in a subdirectory.

echo "`wasmer -V` | `rustc -V` | `uname -m`"
wasmer 1.0.0-alpha4 | rustc 1.47.0 (18bf6b4f0 2020-10-07) | x86_64

Steps to reproduce

1. Download uutils.wasm from WAPM
2. Create directory dir with a sample file foo in it
3. Run wasmer --dir=./dir uutils.wasm -- mv dir/foo dir/bar

Expected behavior

File ./dir/foo is renamed to ./dir/bar

Actual behavior

File ./dir/foo is renamed to ./bar

Additional context

wasmer --dir=./dir uutils.wasm -- mv dir/dir2/foo dir/dir2/bar works correctly

[MarkMcCaskey]

Thanks for the bug report! That seems like a fairly important bug (breaking the filesystem sandbox), I'll make sure we stress test our sandboxing more