enh: add data-handler when attached to el

Also provide a data-handler attribute to the viewer div
when the viewer is attached to a dom element other than the modal.

Signed-off-by: Max <[email protected]>

Author: max-nextcloud

js/viewer-main.js

@@ -22,7 +22,9 @@
  -->
 
 <template>
-	<div v-if="el" id="viewer">
+	<div v-if="el"
+		id="viewer"
+		:data-handler="handlerId" >
 		<component :is="currentFile.modal"
 			v-if="!currentFile.failed"
 			:key="currentFile.fileid"