Fix theming chaining

Signed-off-by: npmbuildbot[bot] <npmbuildbot[bot]@users.noreply.github.com>

Author: skjnldsv

.eslintrc.js

@@ -3,8 +3,9 @@ module.exports = {
 		appVersion: true,
 		isTesting: true,
 		PLYR_ICONS: true,
+		oc_defaults: true,
 	},
 	extends: [
 		'@nextcloud',
 	],
-};
+}

js/viewer-main.js

@@ -455,7 +455,7 @@ export default {
 		},
 
 		updateTitle(fileName) {
-			document.title = `${fileName} - ${OCA.Theming.name}`
+			document.title = `${fileName} - ${OCA.Theming?.name || oc_defaults.name}`
 		},
 
 		/**