Version tested: 2022.2.a16 (17114ee23d5f) + HDRP from Packman

Steps to reproduce: 

1) Simply create an empty HDRP project

2) Create a decal material, a decal project and assign mew material to it

3) Delete the decal

4) Observe that projector is showing Material missing and render loop breaks

Note: Same happens with decal SG

Proposed result: projector fallbacks to default decal mat to avoid this.

 
{code:java}
MissingReferenceException: The object of type 'Material' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Rendering.HighDefinition.DecalSystem+DecalSet.UpdateCachedDrawOrder () (at D:/GIT/unity/Packages/com.unity.render-pipelines.high-definition/Runtime/Material/Decal/DecalSystem.cs:507)
UnityEngine.Rendering.HighDefinition.DecalSystem.CreateDrawData () (at D:/GIT/unity/Packages/com.unity.render-pipelines.high-definition/Runtime/Material/Decal/DecalSystem.cs:1110)
UnityEngine.Rendering.HighDefinition.HDRenderPipeline.ExecuteRenderRequest (UnityEngine.Rendering.HighDefinition.HDRenderPipeline+RenderRequest renderRequest, UnityEngine.Rendering.ScriptableRenderContext renderContext, UnityEngine.Rendering.CommandBuffer cmd, UnityEngine.Rendering.HighDefinition.AOVRequestData aovRequest) (at D:/GIT/unity/Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipeline.cs:2133)
UnityEngine.Rendering.HighDefinition.HDRenderPipeline.Render (UnityEngine.Rendering.ScriptableRenderContext renderContext, System.Collections.Generic.List`1[T] cameras) (at D:/GIT/unity/Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipeline.cs:2006)
UnityEngine.Rendering.RenderPipeline.InternalRender (UnityEngine.Rendering.ScriptableRenderContext context, System.Collections.Generic.List`1[T] cameras) (at <facf35b0ea244f54b1444810b978175e>:0)
UnityEngine.Rendering.RenderPipelineManager.DoRenderLoop_Internal (UnityEngine.Rendering.RenderPipelineAsset pipe, System.IntPtr loopPtr, System.Collections.Generic.List`1[T] renderRequests, Unity.Collections.LowLevel.Unsafe.AtomicSafetyHandle safety) (at <facf35b0ea244f54b1444810b978175e>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&){code}