dpkg-source: fix initialization of diff-ignore in 1.0 format

Commit 3378e8fa435abe79e9bd3cea07b02f562b906695 broke
"dpkg-source -i -b" on version 1.0 source packages. This restores it.

scripts/Dpkg/Source/Package/V1.pm

@@ -43,7 +43,11 @@ sub init_options {
     my ($self) = @_;
     # Don't call $self->SUPER::init_options() on purpose, V1.0 has no
     # ignore by default
-    $self->{'options'}{'diff_ignore_regexp'} = '(?:^|/)debian/source/local-options$';
+    if (defined $self->{'options'}{'diff_ignore_regexp'}) {
+	$self->{'options'}{'diff_ignore_regexp'} .= '|(?:^|/)debian/source/local-options$';
+    } else {
+	$self->{'options'}{'diff_ignore_regexp'} = '(?:^|/)debian/source/local-options$';
+    }
     $self->{'options'}{'sourcestyle'} ||= 'X';
     $self->{'options'}{'skip_debianization'} ||= 0;
 }