Fixed #2995 execution of 'after_cd' hooks

Fix for #2995
Problem description:

`rmv_path/scripts/hook` ( http://git.io/PwckwQ ) contains:
```bash
hooks=( "$rvm_hooks_path")
[[ "$PWD/.rvm/hooks" == "$rvm_hooks_path" ]] ||
  hooks+=( "$PWD/.rvm/hooks" )

_hooks_list=($(
  __rvm_find -L "${hooks[@]}" -iname "$rvm_hook*" -type f 2>/dev/null
))
```

but when env is not loaded `$rvm_hooks_path` is undefined. This leads
to `"${hooks[@]}"` contains a space and `find` will fail with
`find: ftsopen: No such file or directory` and tnx to `2>/dev/null`
error will be invisible.