fix black screen in XR when HDRP package is present but not used (#137)

Author: fabien-unity

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -532,6 +532,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed culling of planar reflection probes that change position (case 1218651)
 - Fixed null reference when processing lightprobe (case 1235285)
 - Fix issue causing wrong planar reflection rendering when more than one camera is present.
+- Fix black screen in XR when HDRP package is present but not used.
 
 ### Changed
 - Color buffer pyramid is not allocated anymore if neither refraction nor distortion are enabled

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/XR/XRSystem.cs

@@ -73,6 +73,8 @@ internal XRSystem(RenderPipelineResources.ShaderResources shaders)
         [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSplashScreen)]
         internal static void XRSystemInit()
         {
+        	if (GraphicsSettings.currentRenderPipeline == null)
+                return;
 
         #if UNITY_2020_2_OR_NEWER
             SubsystemManager.GetSubsystems(displayList);