[FIX] web_editor: do not break labels' texts into <p/>

When editing the content of a <label/> which has XML branding (first
DOM element which is editable in its hierarchy), a <p/> element was
added inside. This behavior is there to automatically add <p/> elements
in empty editable <div/> / <section/> elements on edition. This should
however not apply on <label/> elements.

addons/web_editor/static/src/js/rte.summernote.js

@@ -428,7 +428,7 @@ $.summernote.pluginEvents.visible = function (event, editor, layoutInfo) {
     if (($node.is('[data-oe-type="html"]') || $node.is('[data-oe-field="arch"]')) &&
         $node.hasClass("o_editable") &&
         !$node[0].children.length &&
-        "h1 h2 h3 h4 h5 h6 p b bold i u code sup strong small pre th td".toUpperCase().indexOf($node[0].nodeName) === -1) {
+        "h1 h2 h3 h4 h5 h6 p b bold i u code sup strong small pre th td label".toUpperCase().indexOf($node[0].nodeName) === -1) {
         var p = $('<p><br/></p>')[0];
         $node.append( p );
         range.createFromNode(p.firstChild).select();