validate that root signatures don't have gaps

code/renderer/rhi_d3d12.cpp

@@ -32,7 +32,6 @@ to do:
 - use Application Verifier to catch issues
 - tone mapping: look at https://github.com/h3r2tic/tony-mc-mapface
 - ubershader PS: run-time alpha test evaluation to reduce PSO count?
-- when creating the root signature, validate that neither of the tables have any gap
 - use root signature 1.1 to use the hints that help the drivers optimize out static resources
 - is it possible to force Resource Binding Tier 2 somehow? are we supposed to run on old HW to test? :(
 	see if WARP allows us to do that?
@@ -3603,6 +3602,7 @@ namespace RHI
 		//
 		// CBV SRV UAV table
 		//
+		uint32_t onePastLastTableIndex = 0;
 		D3D12_DESCRIPTOR_RANGE genericRanges[ARRAY_LEN(rhiDesc.genericRanges)] = {};
 		for(uint32_t rangeIndex = 0; rangeIndex < rhiDesc.genericRangeCount; ++rangeIndex)
 		{
@@ -3620,7 +3620,13 @@ namespace RHI
 				r.RegisterSpace = 1;
 			}
 			rhiSignature.genericDescCount += rIn.count;
+			onePastLastTableIndex = max(onePastLastTableIndex, rIn.firstIndex + rIn.count);
 		}
+
+		// if you trigger this, you have at least 1 gap in your root signature
+		Q_assert(onePastLastTableIndex == rhiSignature.genericDescCount);
+		rhiSignature.genericDescCount = onePastLastTableIndex; // safety net...
+
 		if(rhiSignature.genericDescCount > 0)
 		{
 			rhiSignature.genericTableIndex = parameterCount;