Method IsFree

3rdparty/d3d12memalloc/src/D3D12MemAlloc.cpp:4634–4634

        void MarkFree() { prevFree = NULL; }
        void MarkTaken() { prevFree = this; }
        bool IsFree() const { return prevFree != this; }
        void*& PrivateData() { D3D12MA_HEAVY_ASSERT(!IsFree()); return privateData; }
        Block*& PrevFree() { return prevFree; }
        Block*& NextFree() { D3D12MA_HEAVY_ASSERT(IsFree()); return nextFree; }