Disallow -0 in algorithm for checking array index (whatwg#517)

Fixes: whatwg#516

index.bs

@@ -132,6 +132,7 @@ urlPrefix: https://tc39.github.io/ecma262/; spec: ECMA-262
         text: IsConstructor; url: sec-isconstructor
         text: IsDataDescriptor; url: sec-isdatadescriptor
         text: IsDetachedBuffer; url: sec-isdetachedbuffer
+        text: IsInteger; url: sec-isinteger
         text: IsSharedArrayBuffer; url: sec-issharedarraybuffer
         text: IteratorStep; url: sec-iteratorstep
         text: IteratorValue; url: sec-iteratorvalue
@@ -12620,11 +12621,13 @@ internal method as follows.
     1.  If <a abstract-op>Type</a>(|P|) is not String, then return <emu-val>false</emu-val>.
     1.  Let |index| be [=!=] <a abstract-op>CanonicalNumericIndexString</a>(|P|).
     1.  If |index| is <emu-val>undefined</emu-val>, then return <emu-val>false</emu-val>.
-    1.  If |index| is less than 0 or is greater than or equal to 2<sup>32</sup> − 1, then return
-        <emu-val>false</emu-val>.
-
-          Note: 2<sup>32</sup> − 1 is the maximum array length allowed by ECMAScript.
+    1.  If <a abstract-op>IsInteger</a>(|index|) is <emu-val>false</emu-val>,
+        then return <emu-val>false</emu-val>.
+    1.  If |index| is −0, then return <emu-val>false</emu-val>.
+    1.  If |index| &lt; 0, then return <emu-val>false</emu-val>.
+    1.  If |index| ≥ 2<sup>32</sup> − 1, then return <emu-val>false</emu-val>.
 
+        Note: 2<sup>32</sup> − 1 is the maximum array length allowed by ECMAScript.
     1.  Return <emu-val>true</emu-val>.
 
 </div>