Fix the deadlock issue during shutdown the system layer

When the app calls PlatformManager's Shutdown API twice,
the function tries to join the abnormal main loop's thread.
Adds the prevent function to avoid this deadlock issue.

src/platform/Tizen/PlatformManagerImpl.cpp

@@ -131,9 +131,17 @@ void PlatformManagerImpl::_Shutdown()
 {
     Internal::GenericPlatformManagerImpl_POSIX<PlatformManagerImpl>::_Shutdown();
 
+    if (mGLibMainLoop == nullptr)
+    {
+        ChipLogError(DeviceLayer, "System Layer is already shutdown.");
+        return;
+    }
+
     g_main_loop_quit(mGLibMainLoop);
     g_main_loop_unref(mGLibMainLoop);
     g_thread_join(mGLibMainLoopThread);
+
+    mGLibMainLoop = nullptr;
 }
 
 CHIP_ERROR PlatformManagerImpl::_GLibMatterContextInvokeSync(CHIP_ERROR (*func)(void *), void * userData)