completion: disable dwim on "git switch -d"

Even though dwim is enabled by default, it will never be done when
--detached is specified. If you force "-d --guess" you will get an error
because --guess then implies -c which cannot be used with -d. So we can
disable dwim in "switch -d". It makes the completion list in this case a
bit shorter.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -2183,6 +2183,10 @@ _git_switch ()
 		fi
 		if [ -z "$(__git_find_on_cmdline "-d --detach")" ]; then
 			only_local_ref=y
+		else
+			# --guess --detach is invalid combination, no
+			# dwim will be done when --detach is specified
+			track_opt=
 		fi
 		if [ $only_local_ref = y -a -z "$track_opt" ]; then
 			__gitcomp_direct "$(__git_heads "" "$cur" " ")"