Use this.content instead of ev.target, which is null

when using converse.js inside a webcomponent

src/converse-chatview.js

@@ -209,7 +209,7 @@
                 },
 
                 setScrollPosition (ev) {
-                    this.model.save('scroll_position', ev.target.scrollTop);
+                    this.model.save('scroll_position', this.content);
                 },
 
                 chooseSkinTone (ev) {

src/converse-mam.js

@@ -253,7 +253,7 @@
 
                 onScroll (ev) {
                     const { _converse } = this.__super__;
-                    if (ev.target.scrollTop === 0 && this.model.messages.length) {
+                    if (this.content.scrollTop === 0 && this.model.messages.length) {
                         const oldest_message = this.model.messages.at(0);
                         const archive_id = oldest_message.get('archive_id');
                         if (archive_id) {