Merge branch 'ak/add-i-empty-candidates' into maint

The interactive "show a list and let the user choose from it"
interface "add -i" used showed and prompted to the user even when
the candidate list was empty, against which the only "choice" the
user could have made was to choose nothing.

* ak/add-i-empty-candidates:
  add -i: return from list_and_choose if there is no candidate

Author: gitster

git-add--interactive.perl

@@ -515,6 +515,9 @@ sub error_msg {
 sub list_and_choose {
 	my ($opts, @stuff) = @_;
 	my (@chosen, @return);
+	if (!@stuff) {
+	    return @return;
+	}
 	my $i;
 	my @prefixes = find_unique_prefixes(@stuff) unless $opts->{LIST_ONLY};
 
@@ -725,6 +728,8 @@ sub add_untracked_cmd {
 	if (@add) {
 		system(qw(git update-index --add --), @add);
 		say_n_paths('added', @add);
+	} else {
+		print "No untracked files.\n";
 	}
 	print "\n";
 }