[FIX] web_editor: ie issue with range within undisplayed

In IE11, when adding a range to a selection that can fail if this range
is not displayed (display non on itself or an ancestor) or is not already
inserted in the dom.

e.g: IE fails in the following situation: http://jsfiddle.net/7cmf2tt9/7/

The feature causing this situation is minimal : it only set the cursor
at the end of a FieldTextHtmlSimple widget (the default widget for
fields.Html). This commit thus only ignore that error.

note: this is not an issue on IE Edge.

closes #9216
opw-652347

addons/web_editor/static/src/js/backend.js

@@ -106,7 +106,10 @@ var FieldTextHtmlSimple = widget.extend({
         var value = this.get('value');
         this.$textarea.val(value || '');
         this.$content.html(this.text_to_html(value));
-        this.$content.focusInEnd();
+        // on ie an error may occur when creating range on not displayed element
+        try {
+            this.$content.focusInEnd();
+        } catch (e) {}
         var history = this.$content.data('NoteHistory');
         if (history && history.recordUndo()) {
             this.$('.note-toolbar').find('button[data-event="undo"]').attr('disabled', false);