only load Sfjs if it is not present

Plus, avoid loading the toolbar if it is no longer on the page

src/Symfony/Bundle/WebProfilerBundle/Resources/views/Profiler/base_js.html.twig

@@ -5,6 +5,7 @@
                 them as JavaScript source code. Always use '/*' comments instead
                 of '//' comments to avoid impossible-to-debug side-effects #}
 
+if (typeof Sfjs === 'undefined') {
     Sfjs = (function() {
         "use strict";
 
@@ -424,6 +425,10 @@
                     'sfwdt' + token,
                     '{{ url("_wdt", { "token": "xxxxxx" })|escape('js') }}'.replace(/xxxxxx/, newToken),
                     function(xhr, el) {
+                        /* Do nothing in the edge case where the toolbar has already been replaced with a new one */
+                        if (!document.getElementById('sfToolbarMainContent-' + newToken)) {
+                            return;
+                        }
 
                         /* Evaluate in global scope scripts embedded inside the toolbar */
                         var i, scripts = [].slice.call(el.querySelectorAll('script'));
@@ -799,5 +804,5 @@
         Sfjs.createTabs();
         Sfjs.createToggles();
     });
-
+}
 /*]]>*/</script>