completion: Lint github-cli completion and use completion_exists

clean_files.txt

@@ -64,6 +64,7 @@ completion/available/conda.completion.bash
 completion/available/consul.completion.bash
 completion/available/docker.completion.bash
 completion/available/gcloud.completion.bash
+completion/available/github-cli.completion.bash
 completion/available/helm.completion.bash
 completion/available/knife.completion.bash
 completion/available/packer.completion.bash

completion/available/github-cli.completion.bash

@@ -1,8 +1,9 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 cite "about-completion"
 about-completion "GitHub CLI completion"
 
 if _binary_exists gh; then
-    complete -p gh &> /dev/null || return
+	# If gh already completed, stop
+	_completion_exists gh && return
 	eval "$(gh completion --shell=bash)"
 fi