[FIX] mail: chatter attachments without thread

This fix prevents the chatter and attachment box
from assuming that there is a mail_thread on the record;

Reason: if a chatter is set on a record that doesn't inherit
mail_thread, the attachment box will generate errors.

closes #31206

addons/mail/static/src/js/chatter.js

@@ -90,6 +90,7 @@ var Chatter = Widget.extend({
         this._$topbar = this.$('.o_chatter_topbar');
         if(!this._disableAttachmentBox) {
             this.$('.o_topbar_right_area').append(QWeb.render('mail.chatter.Attachment.Button', {
+                displayCounter: !!this.fields.thread,
                 count: this.record.data.message_attachment_count || 0,
             }));
         }
@@ -362,7 +363,9 @@ var Chatter = Widget.extend({
         if (this._isAttachmentBoxOpen) {
             this._fetchAttachments().then(this._openAttachmentBox.bind(this));
         }
-        this.trigger_up('reload', { fieldNames: ['message_attachment_count'] });
+        if (this.fields.thread) {
+            this.trigger_up('reload', { fieldNames: ['message_attachment_count'] });
+        }
     },
     /**
      * @private
@@ -490,7 +493,9 @@ var Chatter = Widget.extend({
                 })
                 .then(function () {
                     self._reloadAttachmentBox();
-                    self.fields.thread.removeAttachments([ev.data.attachmentId]);
+                    if (self.fields.thread) {
+                        self.fields.thread.removeAttachments([ev.data.attachmentId]);
+                    }
                     self.trigger_up('reload');
                 });
             }

addons/mail/static/src/xml/chatter.xml

@@ -105,11 +105,17 @@
 
     </t>
 
+    <!--
+        Chatter attachment paperclip button.
+
+        @param {boolean} [displayCounter]
+        @param {integer} [count]
+    -->
     <t t-name="mail.chatter.Attachment.Button">
         <button class="btn btn-link o_chatter_button_attachment" title="View all the attachments of the current record">
             <span>
                 <i class="fa fa-paperclip"/>
-                <span class="o_chatter_attachment_button_count">
+                <span t-if="displayCounter" class="o_chatter_attachment_button_count">
                     <t t-esc="count"/>
                 </span>
             </span>