Using CHANNEL_PRINTS to transfer printbuffers to stdout is now working.

luprex/cpp/core/lpxserver.cpp

@@ -202,6 +202,7 @@ public:
                 if (print_channeler_.channel(master_->get_printbuffer(admin_id_), retpk)) {
                     master_->invoke(print_channeler_.invocation(admin_id_));
                 }
+                set_have_prints(false);
                 break;
             }
             default: {
@@ -354,6 +355,9 @@ public:
             }
         }
         util::remove_marked_items(http_server_channels_);
+
+        // Notify the driver if there are any prints.
+        set_have_prints(print_channeler_.have_prints(master_->get_printbuffer(admin_id_)));
     }
 };