Fix not showing device in Unity 5.6 w/ SteamVR plugin v1.2.3

SteamVR v1.2.3 NewPosesUpdater doesn't work because OnCameraPreCull
callback (called onc per camera e per frame) in Unity 5.6 seems doesn't report VR camera as CameraType.VR
(CameraType.Game instead), and the updater skip them.
After Unity 2017.2 updating VR device pose should use onBeforeRender callback
instead (called once per frame)

close #28

Author: lawwong

Assets/HTC.UnityPlugin/VRModule/VRModuleManager.cs

@@ -186,7 +186,9 @@ private void ActivateModule(VRModuleActiveEnum module)
             {
 #if VIU_STEAMVR
                 case VRModuleActiveEnum.SteamVR:
-#if VIU_STEAMVR_1_2_0_OR_NEWER
+#if VIU_STEAMVR_1_2_3_OR_NEWER && !UNITY_2017_1_OR_NEWER
+                    Camera.onPreCull += OnCameraPreCull;
+#elif VIU_STEAMVR_1_2_0_OR_NEWER
                     SteamVR_Events.NewPoses.AddListener(OnSteamVRNewPose);
 #elif VIU_STEAMVR_1_1_1
                     SteamVR_Utils.Event.Listen("new_poses", OnSteamVRNewPoseArgs);
@@ -226,7 +228,7 @@ private void OnCameraPreCull(Camera cam)
             var thisFrame = Time.frameCount;
             if (m_poseUpdatedFrame == thisFrame) { return; }
 
-            if (cam.cameraType != CameraType.Game) { return; }
+            if (cam.cameraType != CameraType.Game && cam.cameraType != CameraType.VR) { return; }
 
             m_poseUpdatedFrame = thisFrame;
             UpdateActiveModuleDeviceState();
@@ -303,7 +305,9 @@ private void DeactivateModule()
             {
 #if VIU_STEAMVR
                 case VRModuleActiveEnum.SteamVR:
-#if VIU_STEAMVR_1_2_0_OR_NEWER
+#if VIU_STEAMVR_1_2_3_OR_NEWER && !UNITY_2017_1_OR_NEWER
+                    Camera.onPreCull -= OnCameraPreCull;
+#elif VIU_STEAMVR_1_2_0_OR_NEWER
                     SteamVR_Events.NewPoses.RemoveListener(OnSteamVRNewPose);
 #elif VIU_STEAMVR_1_1_1
                     SteamVR_Utils.Event.Remove("new_poses", OnSteamVRNewPoseArgs);

Assets/HTC.UnityPlugin/ViveInputUtility/Scripts/VIUVersion.cs

@@ -6,6 +6,6 @@ namespace HTC.UnityPlugin.Vive
 {
     public static class VIUVersion
     {
-        public static readonly Version current = new Version("1.8.0.8");
+        public static readonly Version current = new Version("1.8.0.9");
     }
 }