Support constant attributes (with a value of zero) (#1066)

* Support constant attributes (with a value of zero)

* Remove extra line

Ryujinx.Graphics.Gpu/Engine/Methods.cs

@@ -532,6 +532,7 @@ namespace Ryujinx.Graphics.Gpu.Engine
                 vertexAttribs[index] = new VertexAttribDescriptor(
                     vertexAttrib.UnpackBufferIndex(),
                     vertexAttrib.UnpackOffset(),
+                    vertexAttrib.UnpackIsConstant(),
                     format);
             }