dpkg-buildpackage: Do not warn on unsigned UNRELEASED builds on -uc or -us

If the user has explicitly requested not to sign the build, do not
complain that we are not going to sign it due to it being UNRELEASED.

Regression introduced in commit 8a8030be47fee6b480905781e56eacc8005227fc.

scripts/dpkg-buildpackage.pl

@@ -332,7 +332,7 @@ if (not $signcommand) {
 } elsif ($signforce) {
     $signsource = 1;
     $signchanges = 1;
-} elsif ($distribution eq 'UNRELEASED') {
+} elsif (($signsource or $signchanges) and $distribution eq 'UNRELEASED') {
     $signreleased = 0;
     $signsource = 0;
     $signchanges = 0;