fix(function): suppress error messages for non-existent functions

Author: akinomyoga

completions/function

@@ -8,7 +8,7 @@ _function()
     if ((cword == 1)); then
         COMPREPLY=($(compgen -A function -- "$cur"))
     else
-        COMPREPLY=("() $(type -- ${words[1]} | command sed -e 1,2d)")
+        COMPREPLY=("() $(type -- "${words[1]}" 2>/dev/null | command sed -e 1,2d)")
     fi
 } &&
     complete -F _function function