completion: bash: add correct suffix in variables

__gitcomp automatically adds a suffix, but __gitcomp_nl and others
don't, we need to specify a space by default.

Can be tested with:

  git config branch.autoSetupMe<tab>

This fix only works for versions of bash greater than 4.0, before that
"local sfx" creates an empty string, therefore the unset expansion
doesn't work. The same happens in zsh.

Therefore we don't add the test for that for now.

The correct fix for all shells requires semantic changes in __gitcomp,
but that can be done later.

Cc: SZEDER Gábor <szeder.dev@gmail.com>
Tested-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -2652,7 +2652,7 @@ __git_complete_config_variable_name ()
 		local pfx="${cur_%.*}."
 		cur_="${cur_#*.}"
 		__gitcomp_direct "$(__git_heads "$pfx" "$cur_" ".")"
-		__gitcomp_nl_append $'autoSetupMerge\nautoSetupRebase\n' "$pfx" "$cur_" "$sfx"
+		__gitcomp_nl_append $'autoSetupMerge\nautoSetupRebase\n' "$pfx" "$cur_" "${sfx- }"
 		return
 		;;
 	guitool.*.*)
@@ -2686,7 +2686,7 @@ __git_complete_config_variable_name ()
 		local pfx="${cur_%.*}."
 		cur_="${cur_#*.}"
 		__git_compute_all_commands
-		__gitcomp_nl "$__git_all_commands" "$pfx" "$cur_" "$sfx"
+		__gitcomp_nl "$__git_all_commands" "$pfx" "$cur_" "${sfx- }"
 		return
 		;;
 	remote.*.*)
@@ -2702,7 +2702,7 @@ __git_complete_config_variable_name ()
 		local pfx="${cur_%.*}."
 		cur_="${cur_#*.}"
 		__gitcomp_nl "$(__git_remotes)" "$pfx" "$cur_" "."
-		__gitcomp_nl_append "pushDefault" "$pfx" "$cur_" "$sfx"
+		__gitcomp_nl_append "pushDefault" "$pfx" "$cur_" "${sfx- }"
 		return
 		;;
 	url.*.*)