Handle empty descriptor sets in pipeline layout

The VSG generates layouts like this when descriptor bindings are dependent on defines, and doesn't generate matching empty BindDescriptorSet instances to go with them.
That disrupts the fix in the previous commit, so they must be handled as if they don't exist.

Even though the pipeline layout says these sets exist, there's no need to bind anything to them as they inherently can't be statically used by the pipeline.

Author: AnyOldName3

include/vsg/state/DescriptorSetLayout.h

@@ -37,6 +37,8 @@ namespace vsg
         /// VkDescriptorSetLayoutCreateInfo settings
         DescriptorSetLayoutBindings bindings;
 
+        virtual bool empty() const { return bindings.empty(); }
+
         /// map the descriptor bindings to the descriptor pool sizes that will be required to represent them.
         void getDescriptorPoolSizes(DescriptorPoolSizes& descriptorPoolSizes);
 

include/vsg/state/ViewDependentState.h

@@ -33,6 +33,8 @@ namespace vsg
     public:
         ViewDescriptorSetLayout();
 
+        bool empty() const override { return false; }
+
         VkDescriptorSetLayout vk(uint32_t deviceID) const override { return _viewDescriptorSetLayout ? _viewDescriptorSetLayout->vk(deviceID) : 0; }
 
         int compare(const Object& rhs_object) const override;

src/vsg/state/PipelineLayout.cpp

@@ -130,7 +130,7 @@ void PipelineLayout::compile(Context& context)
         for (auto dsl : setLayouts)
         {
             if (dsl) dsl->compile(context);
-            descriptorSetSlots.push_back(dsl != nullptr);
+            descriptorSetSlots.push_back(dsl != nullptr && !dsl->empty());
         }
         _implementation[context.deviceID] = PipelineLayout::Implementation::create(context.device, setLayouts, pushConstantRanges, flags);
     }