* Semicolon not needed at end of command.
* `[@]` not needed if variable is not within `""`. Anyway, the quotes
  would only serve to expand empty-string entries in the array, which
  should not exist here.
* Simplify test for occurence of `_direnv_hook` in array. This syntax
  also works with what was previously reported in #803:

      $ set -euo pipefail
      $ typeset -ag precmd_functions
      $ print $precmd_functions

      $ print ${precmd_functions[(I)_direnv_hook]}
      0
      $ print "${precmd_functions[(r)_direnv_hook]+1}"

      $ print ${precmd_functions[(r)_direnv_hook]}
      zsh: precmd_functions[(r)_direnv_hook]: parameter not set