added checks for wrong tldr --list output in completions

[iliya-malecki]

when tldr-pages doesnt exist (yet, as in, new installation), tldr --list will output something that makes no sense for the completions. I am not qualified to do a real fix, but the completions output did bug me enough to patch it for zsh and bash. I tried to patch it for fish as well but couldnt get the original completion to work so im leaving the problem for actual fish users.

TL;DR:
Purpose: reduce annoyance during first use, which is important for user-friendliness
Method: patch completions with a simple if-no-error check, for zsh and bash.

[niklasmohrin]

Thanks!

For fish, it could probably be something like

if set entries (tldr --list 2>/dev/null)
    string replace -a -i -r "\,\s" "\n" $entries
end

[niklasmohrin]

As fish is addressed in #331, I am fine with merging this as is

[dbrgn]

As with Fish, I don't know much about completion files, but I trust your judgement (and otherwise we can still fix it, if there are edge cases that aren't yet covered) 🙂