[FIX] mail: prevents traceback when clicking attachment unlink button

Before this commit, quickly clicking on the unlink button of an
attachment could result in a traceback if the click happened right
after the deletion of attachment but before the rendering of the DOM.

part of task-2363522

closes odoo/odoo#63447

X-original-commit: 1858184394342f24f5456728c4255f9980220c20
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/components/attachment/attachment.js

@@ -131,6 +131,9 @@ class Attachment extends Component {
      */
     _onClickUnlink(ev) {
         ev.stopPropagation();
+        if (!this.attachment) {
+            return;
+        }
         if (this.attachment.isLinkedToComposer) {
             this.attachment.remove();
             this.trigger('o-attachment-removed', { attachmentLocalId: this.props.attachmentLocalId });