update: added FixedQuaternion.Zero

Author: mrdav30

src/FixedMathSharp/Numerics/FixedQuaternion.cs

@@ -20,6 +20,11 @@ public struct FixedQuaternion : IEquatable<FixedQuaternion>
         /// </summary>
         public static readonly FixedQuaternion Identity = new FixedQuaternion(Fixed64.Zero, Fixed64.Zero, Fixed64.Zero, Fixed64.One);
 
+        /// <summary>
+        /// Empty quaternion (0, 0, 0, 0).
+        /// </summary>
+        public static readonly FixedQuaternion Zero = new FixedQuaternion(Fixed64.Zero, Fixed64.Zero, Fixed64.Zero, Fixed64.Zero);
+
         #endregion
 
         #region Constructors