Suppress possible warnings after update

Prevent JavaScript errors when the shortcuts have not been defined in
the config file.
https://github.com/FreshRSS/FreshRSS/issues/733

app/views/helpers/javascript_vars.phtml

@@ -35,20 +35,20 @@ echo 'var context={',
 "},\n";
 
 echo 'shortcuts={',
-	'mark_read:"', $s['mark_read'], '",',
-	'mark_favorite:"', $s['mark_favorite'], '",',
-	'go_website:"', $s['go_website'], '",',
-	'prev_entry:"', $s['prev_entry'], '",',
-	'next_entry:"', $s['next_entry'], '",',
-	'first_entry:"', $s['first_entry'], '",',
-	'last_entry:"', $s['last_entry'], '",',
-	'collapse_entry:"', $s['collapse_entry'], '",',
-	'load_more:"', $s['load_more'], '",',
-	'auto_share:"', $s['auto_share'], '",',
-	'focus_search:"', $s['focus_search'], '",',
-	'user_filter:"', $s['user_filter'], '",',
-	'help:"', $s['help'], '",',
-	'close_dropdown:"', $s['close_dropdown'], '"',
+	'mark_read:"', @$s['mark_read'], '",',
+	'mark_favorite:"', @$s['mark_favorite'], '",',
+	'go_website:"', @$s['go_website'], '",',
+	'prev_entry:"', @$s['prev_entry'], '",',
+	'next_entry:"', @$s['next_entry'], '",',
+	'first_entry:"', @$s['first_entry'], '",',
+	'last_entry:"', @$s['last_entry'], '",',
+	'collapse_entry:"', @$s['collapse_entry'], '",',
+	'load_more:"', @$s['load_more'], '",',
+	'auto_share:"', @$s['auto_share'], '",',
+	'focus_search:"', @$s['focus_search'], '",',
+	'user_filter:"', @$s['user_filter'], '",',
+	'help:"', @$s['help'], '",',
+	'close_dropdown:"', @$s['close_dropdown'], '"',
 "},\n";
 
 echo 'url={',