Update AWS completion (#6745)

plugins/aws/aws.plugin.zsh

@@ -42,11 +42,11 @@ function aws_profiles {
 
 compctl -K aws_profiles asp
 
-if _homebrew-installed && _awscli-homebrew-installed ; then
+if which aws_zsh_completer.sh &>/dev/null; then
+  _aws_zsh_completer_path=$(which aws_zsh_completer.sh 2>/dev/null)
+elif _homebrew-installed && _awscli-homebrew-installed; then
   _aws_zsh_completer_path=$_brew_prefix/libexec/bin/aws_zsh_completer.sh
-else
-  _aws_zsh_completer_path=$(which aws_zsh_completer.sh)
 fi
 
-[ -x $_aws_zsh_completer_path ] && source $_aws_zsh_completer_path
+[ -n "$_aws_zsh_completer_path" ] && [ -x $_aws_zsh_completer_path ] && source $_aws_zsh_completer_path
 unset _aws_zsh_completer_path