Use our metadata thread-safe mutex for the new check, seems to work

Signed-off-by: falkTX <falktx@falktx.com>

source/backend/engine/CarlaEngineJack.cpp

@@ -4262,17 +4262,20 @@ private:
 
                 case PostPonedJackEvent::kTypeClientPositionChange:
                 {
-                    /* FIXME there is something seriously wrong on the JACK side if we try to do this...
                     char uuidstr[JACK_UUID_STRING_SIZE];
                     carla_zeroStruct(uuidstr);
                     jackbridge_uuid_unparse(ev.clientPositionChange.uuid, uuidstr);
 
-                    const char* const clientname = jackbridge_get_client_name_by_uuid(fClient, uuidstr);
-                    CARLA_SAFE_ASSERT_CONTINUE(clientname != nullptr && clientname[0] != '\0');
+                    if (clientsToIgnore.count() != 0)
+                    {
+                        const CarlaRecursiveMutexLocker crml(fThreadSafeMetadataMutex);
 
-                    if (clientsToIgnore.contains(clientname))
-                        continue;
-                    */
+                        const char* const clientname = jackbridge_get_client_name_by_uuid(fClient, uuidstr);
+                        CARLA_SAFE_ASSERT_CONTINUE(clientname != nullptr && clientname[0] != '\0');
+
+                        if (clientsToIgnore.contains(clientname))
+                            continue;
+                    }
 
                     handleJackClientPositionChangeCallback(ev.clientPositionChange.uuid);
                     break;