Doesn't disambiguate between 'external command failed' and 'command not found'

An external git-whatever command which fails to run gets reported as not having been found, and suggests ... exactly what you just ran. If you miss the first line of the output, this can be extremely confusing -- and "is not a git command" is somewhat misleading:

        umgah ~ $ cat bin/git-bogus
        #!/usr/bin/env nonexistant
        echo "yay"
        
        umgah ~ $ git bogus
        /usr/bin/env: nonexistant: No such file or directory
        git: 'bogus' is not a git command. See 'git --help'.
        
        Did you mean this?
        	bogus

I've no patch right now, but I thought I'd report the frustration, in
case someone else wanted to get to it first.
 - Alex