Fix reverse HLG transform

The +b needs to happen outside of the exp() call to be the reverse of the original HLG.

css-color-hdr/Overview.bs

@@ -578,7 +578,7 @@ Predefined color spaces for HDR: {#predefined-HDR}
 			E = (Edash ** 2) / 3;
 		}
 		else {
-			E = Math.exp(((Edash - c) / a) + b) / 12;
+			E = (Math.exp((Edash - c) / a) + b) / 12;
 		}
 	</pre>