Query subgroup size control features only if VK_EXT_subgroup_size_control is supported (#966)
Query subgroup size control features only if VK_EXT_subgroup_size_control is supported (#966)

Running standalone Amber using SwiftShader was causing an assert because VkPhysicalDeviceSubgroupSizeControlFeaturesEXT struct was added to a pNext chain for vkGetPhysicalDeviceFeatures2 although SwiftShader doesn't support VK_EXT_subgroup_size_control extension. Now the struct is added to the chain only when the extension is supported.
google/amber,google/amber,google/amber,google/amber,google/amber