Fix array indexing crashes, ditch a lot of messing with UAV start slot

* The UAV array is provided as we expect it - with UAVs from 0 onwards
  even if their 'slots' are 4, 5, 6 etc or whatever. UAVStartSlot is
  the slot of the 0th UAV.

renderdoc/api/replay/d3d11_pipestate.h

@@ -203,6 +203,9 @@ struct D3D11PipelineState
 
 	struct OutputMerger
 	{
+		OutputMerger()
+			: UAVStartSlot(0), DepthReadOnly(false), StencilReadOnly(false) {}
+
 		struct DepthStencilState
 		{
 			DepthStencilState()