Fix HTML-CSS bounding boxes for annotation-xml nodes when used illegally as first semantics child.

Author: dpvc

unpacked/jax/output/HTML-CSS/autoload/annotation-xml.js

@@ -48,9 +48,11 @@ MathJax.Hub.Register.StartupHook("HTML-CSS Jax Ready",function () {
     toHTML: function (span,encoding) {
       for (var i = 0, m = this.data.length; i < m; i++) 
         {span.appendChild(this.data[i].cloneNode(true))}
-      span.bbox.w = HTMLCSS.getW(span); span.bbox.rw = span.bbox.w;
+      var bbox = span.bbox; span.bbox = null;
+      bbox.rw = bbox.w = HTMLCSS.getW(span);
       var HD = HTMLCSS.getHD(span);
-      span.bbox.h = HD.h; span.bbox.d = HD.d;
+      bbox.h = HD.h; bbox.d = HD.d;
+      span.bbox = bbox;
     }
   });