Let the OTR code for adding a button mirror the spoiler way

src/converse-otr.js

@@ -419,13 +419,10 @@
                     }
                 },
 
-                renderToolbar (toolbar, options) {
+                addOTRToolbarButton (options) {
                     const { _converse } = this.__super__,
-                        { __ } = _converse;
-                    if (!_converse.show_toolbar) {
-                        return;
-                    }
-                    const data = this.model.toJSON();
+                          { __ } = _converse,
+                          data = this.model.toJSON();
                     options = _.extend(options || {}, {
                         FINISHED,
                         UNENCRYPTED,
@@ -443,13 +440,17 @@
                         otr_tooltip: this.getOTRTooltip(),
                         otr_translated_status: OTR_TRANSLATED_MAPPING[data.otr_status],
                     });
-                    this.__super__.renderToolbar.apply(this, arguments);
                     this.el.querySelector('.chat-toolbar').insertAdjacentHTML(
                         'beforeend',
                         tpl_toolbar_otr(
                             _.extend(this.model.toJSON(), options || {})
                         ));
-                    return this;
+                },
+
+                renderToolbar (toolbar, options) {
+                    const result = this.__super__.renderToolbar.apply(this, arguments);
+                    this.addOTRToolbarButton(options);
+                    return result;
                 }
             }
         },