fix(files_sharing): ensure that external section is mounted

Make sure the external section is mounted before trying to assign it the
node prop.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

apps/files_sharing/src/components/SidebarTabExternal/SidebarTabExternalSection.vue

@@ -28,6 +28,8 @@ const props = defineProps({
 // TOOD: Remove with Vue 3
 const sectionElement = ref()
 watchEffect(() => {
-	sectionElement.value.node = props.node
+	if (sectionElement.value) {
+		sectionElement.value.node = props.node
+	}
 })
 </script>