Issue #3315055: Don't create an override button for the #override-mode-tray element in JS

Closes #3315055

js/override_mode.js

@@ -40,7 +40,7 @@
         // Flag that Override Mode is enabled.
         Drupal.behaviors.OverrideUiBehaviour.overrideMode = true;
 
-        const overridableTemplates = document.querySelectorAll('[data-override-mode]');
+        const overridableTemplates = document.querySelectorAll('[data-override-mode]:not(#override-mode-tray)');
         const list = document.createElement('ul');
 
         overridableTemplates.forEach(function (overridableTemplate) {
@@ -148,6 +148,7 @@
         return;
       }
       let element = e.target;
+
       let pairedButton = document.querySelector('[data-override-mode="' + this.dataset.overrideMode + '"].override-button');
 
       if (e.type === 'mouseover') {
@@ -179,7 +180,7 @@
         },
       };
       let variables = document.querySelector('script[data-uuid="' + settings.uuid + '"]');
-      if (typeof variables.textContent !== 'undefined') {
+      if (variables !== null && typeof variables.textContent !== 'undefined') {
         ajaxConfig.submit = {variables: variables.textContent};
       }
       let ajax = Drupal.ajax(ajaxConfig);