Fix mac crash

Author: atoko

ResourceManager.cpp

@@ -120,6 +120,7 @@ ResourceManager::ResourceManager()
     detection_percent           = 100;
     detection_string            = "";
     detection_is_required       = false;
+    DetectDevicesThread         = nullptr;
     dynamic_detectors_processed = false;
     init_finished               = false;
     background_thread_running    = true;

ResourceManager.h

@@ -291,6 +291,7 @@ class ResourceManager: public ResourceManagerInterface
     | Detection Thread and Detection State                                                  |
     \*-------------------------------------------------------------------------------------*/
     std::thread *                               DetectDevicesThread;
+    std::thread *                               DetectDevicesThread; // Used for rescan
     std::mutex                                  DetectDeviceMutex;
     std::function<void()>                       ScheduledBackgroundFunction;
     std::mutex                                  BackgroundThreadStateMutex;