Don't sign to already signed rpm when key is missing

It causes following the error for example.

  % rpm --checksig repositories/centos/5/source/SRPMS/MySQL-5.5.21-1.rhel5.src.rpm
  error: repositories/centos/5/source/SRPMS/MySQL-5.5.21-1.rhel5.src.rpm: sigh tags: BAD, no. of tags(33) out of range

packages/yum/sign-rpm.sh

@@ -24,7 +24,7 @@ run()
 unsigned_rpms()
 {
     while read rpm; do
-	rpm --checksig "$rpm" | grep -v 'gpg OK' | cut -d":" -f1
+	rpm --checksig "$rpm" | grep -v 'gpg OK' | grep -v 'MISSING KEYS' | cut -d":" -f1
     done
 }