Editorial: (Exponentiation) Add NaN to exponent values whose behavior…

… deviates from IEEE 754-2008 (tc39#1228)

This oversight was discovered and reported to me by James Clark ([email protected]).

spec.html

@@ -1591,7 +1591,7 @@ <h1>Number::exponentiate ( _base_, _exponent_ )</h1>
             <li>If _base_ &lt; 0 and _base_ is finite and _exponent_ is finite and _exponent_ is not an integer, the result is *NaN*.</li>
           </ul>
           <emu-note>
-            <p>The result of _base_ `**` _exponent_ when _base_ is *1* or *-1* and _exponent_ is *+Infinity* or *-Infinity* differs from IEEE 754-2019. The first edition of ECMAScript specified a result of *NaN* for this operation, whereas later versions of IEEE 754-2019 specified *1*. The historical ECMAScript behaviour is preserved for compatibility reasons.</p>
+            <p>The result of _base_ `**` _exponent_ when _base_ is *1* or *-1* and _exponent_ is *+Infinity* or *-Infinity*, or when _base_ is *1* and _exponent_ is *NaN*, differs from IEEE 754-2019. The first edition of ECMAScript specified a result of *NaN* for this operation, whereas later versions of IEEE 754-2019 specified *1*. The historical ECMAScript behaviour is preserved for compatibility reasons.</p>
           </emu-note>
         </emu-clause>