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

* Support constant attributes (with a value of zero)

* Remove extra line

Ryujinx.Graphics.Gpu/State/VertexAttribState.cs

@@ -16,6 +16,15 @@ namespace Ryujinx.Graphics.Gpu.State
             return (int)(Attribute & 0x1f);
         }
 
+        /// <summary>
+        /// Unpacks the attribute constant flag.
+        /// </summary>
+        /// <returns>True if the attribute is constant, false otherwise</returns>
+        public bool UnpackIsConstant()
+        {
+            return (Attribute & 0x40) != 0;
+        }
+
         /// <summary>
         /// Unpacks the offset, in bytes, of the attribute on the vertex buffer.
         /// </summary>