Make isviewer a sink to file

src/backend/core/mmio/PI.cpp

@@ -321,7 +321,8 @@ void PI::BusWrite<u32, false>(u32 addr, u32 val) {
         if (val < CART_ISVIEWER_SIZE) {
           std::string message(val + 1, 0);
           std::copy_n(mem.isviewer.begin(), val, message.begin());
-          always("{}", message);
+          mem.isviewer_sink << message;
+          mem.isviewer_sink.flush();
         } else {
           panic("ISViewer buffer size is emulated at {} bytes, but received a flush command for {} bytes!",
                       CART_ISVIEWER_SIZE, val);