add trailing else block to catch everything else

[tomeichlersmith]

I've been annoyed when I notice I can't tab complete path names in positions after the second position and so adding this final else block restore default bash completion for any situation that isn't specific to denv.

[tomeichlersmith]

I was able to do a simple confirmation that this extra else block works as long as the completions are re-initialized (new terminal or re-sourcing of completion attaching script).

tom@nixos:~/code/denv$ git branch
  102-uid-on-macos
  default-comp-by-default
* main
tom@nixos:~/code/denv$ . completions/denv 
tom@nixos:~/code/denv$ denv bash man/ ma # pressing Tab has no response^C
tom@nixos:~/code/denv$ git switch default-comp-by-default 
Switched to branch 'default-comp-by-default'
Your branch is up to date with 'origin/default-comp-by-default'.
tom@nixos:~/code/denv$ . completions/denv 
tom@nixos:~/code/denv$ denv bash man/ man/ # pressing Tab completes directory like first argument