check array length to avoid removing empty list of packages

Author: lexming

ncm-spma/src/main/perl/spma/yum.pm

@@ -907,7 +907,9 @@ sub update_pkgs
         $to_rm = $self->packages_to_remove($wanted);
         defined($to_rm) or return 0;
         $self->spare_dependencies($to_rm, $to_install, $error_is_warn);
-        $tx = $self->schedule(REMOVE, $to_rm);
+        if (scalar(@$to_rm) > 0) {
+            $tx = $self->schedule(REMOVE, $to_rm);
+        }
     }
 
     $tx .= $self->schedule(INSTALL, $to_install);