Fix bash completion on systems where extglob is not set

Signed-off-by: Harald Albers <github@albersweb.de>

contrib/completion/bash/docker

@@ -49,6 +49,9 @@
 # options immediately following their corresponding long form.
 # This order should be applied to lists, alternatives and code blocks.
 
+__docker_previous_extglob_setting=$(shopt -p extglob)
+shopt -s extglob
+
 __docker_q() {
 	docker ${host:+-H "$host"} ${config:+--config "$config"} 2>/dev/null "$@"
 }
@@ -1890,4 +1893,7 @@ _docker() {
 	return 0
 }
 
+eval "$__docker_previous_extglob_setting"
+unset __docker_previous_extglob_setting
+
 complete -F _docker docker