Change reserved pointerId for non-pointer events from 0 to -1

Relates to #343

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@@ -823,7 +823,7 @@ <h3>The <dfn><code>click</code>, <code>auxclick</code>, and <code>contextmenu</c
                    The type of these events MUST be <code>PointerEvent</code> but the dispatch process is going to match that of the original specification.
                    For these events, all <code>PointerEvent</code> specific attributes (defined in this spec) other than <code>pointerId</code> and <code>pointerType</code> will have their default values.
                    The <code>pointerId</code> and <code>pointertType</code> of these events MUST be the same as the PointerEvents that caused these events if they are generated by a pointing device.
-                   If the events are generated by a non-pointing device (such as voice recognition software or a keyboard interaction), <code>pointerId</code> MUST be 0 and <code>pointerType</code> MUST be an empty string.</p>
+                   If the events are generated by a non-pointing device (such as voice recognition software or a keyboard interaction), <code>pointerId</code> MUST be <code>-1</code> and <code>pointerType</code> MUST be an empty string.</p>
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