restore the verification before opening a new picker

src/plugins/sib-reactions.js

@@ -217,11 +217,12 @@ converse.plugins.add('sib-reactions', {
         ev.preventDefault();
 
         // Avoid an error when opening a new picker
-        if (this.querySelector('emoji-picker')) {
+        if (document.querySelector('.emoji-reaction-select')) {
           return;
         }
 
         const picker = new Picker();
+        picker.classList.add('emoji-reaction-select');
 
         picker.addEventListener('emoji-click', e => {
           const emoji = e.detail.unicode;