Change xyY_to_XYZ function to prevent negative floating point error i…

…n some cases.

Python Example:
1 - 0.680 - 0.320 = -5.551115123125783e-17;
1 - (0.680 + 0.320) = 0.0

colour/models/cie_xyy.py

@@ -149,7 +149,7 @@ def xyY_to_XYZ(xyY: ArrayLike) -> NDArrayFloat:
     with sdiv_mode():
         Y_y = sdiv(Y, y)
 
-    XYZ = tstack([x * Y_y, Y, (1 - x - y) * Y_y])
+    XYZ = tstack([x * Y_y, Y, (1 - (x + y)) * Y_y])
 
     return from_range_1(XYZ)