Add some potential TODO for another way to track devices without serial

plugins/usbdmx/AVLdiyD512Factory.cpp

@@ -63,6 +63,9 @@ bool AVLdiyD512Factory::DeviceAdded(
   // Some AVLdiy devices don't have serial numbers. Since there isn't another
   // good way to uniquely identify a USB device, we only support one of these
   // types of devices per host.
+  // TODO(Peter): We could instead use the device & bus number (like the
+  // Eurolite plugin). You could use more than one device, but the patch
+  // wouldn't follow if you plugged it into a different port
   if (info.serial.empty()) {
     if (m_missing_serial_number) {
       OLA_WARN << "Failed to read serial number or serial number empty. "

plugins/usbdmx/AnymauDMXFactory.cpp

@@ -63,6 +63,9 @@ bool AnymauDMXFactory::DeviceAdded(
   // Some Anyma devices don't have serial numbers. Since there isn't another
   // good way to uniquely identify a USB device, we only support one of these
   // types of devices per host.
+  // TODO(Peter): We could instead use the device & bus number (like the
+  // Eurolite plugin). You could use more than one device, but the patch
+  // wouldn't follow if you plugged it into a different port
   if (info.serial.empty()) {
     if (m_missing_serial_number) {
       OLA_WARN << "Failed to read serial number or serial number empty. "

plugins/usbdmx/DMXCreator512BasicFactory.cpp

@@ -55,6 +55,9 @@ bool DMXCreator512BasicFactory::DeviceAdded(
   // vendor and product ids. Also, since DMXCreator 512 Basic devices don't have
   // serial numbers and there is no other good way to uniquely identify a USB
   // device, we only support one of these types of devices per host.
+  // TODO(Peter): We could instead use the device & bus number (like the
+  // Eurolite plugin). You could use more than one device, but the patch
+  // wouldn't follow if you plugged it into a different port
   if (info.serial.empty()) {
     if (m_missing_serial_number) {
       OLA_WARN << "We can only support one device without a serial number.";

plugins/usbdmx/ScanlimeFadecandyFactory.cpp

@@ -64,6 +64,9 @@ bool ScanlimeFadecandyFactory::DeviceAdded(
   // Fadecandy devices may be missing serial numbers. Since there isn't another
   // good way to uniquely identify a USB device, we only support one of these
   // types of devices per host.
+  // TODO(Peter): We could instead use the device & bus number (like the
+  // Eurolite plugin). You could use more than one device, but the patch
+  // wouldn't follow if you plugged it into a different port
   if (info.serial.empty()) {
     if (m_missing_serial_number) {
       OLA_WARN << "Failed to read serial number or serial number empty. "