[minor] fixes for https://github.com/frappe/erpnext/issues/8638

frappe/core/doctype/file/file.js

@@ -23,7 +23,7 @@ frappe.ui.form.on("File", "refresh", function(frm) {
 		wrapper.empty();
 	}
 
-	if(frm.doc.file_name.split('.').splice(-1)[0]==='zip') {
+	if(frm.doc.file_name && frm.doc.file_name.split('.').splice(-1)[0]==='zip') {
 		frm.add_custom_button(__('Unzip'), function() {
 			frappe.call({
 				method: "frappe.core.doctype.file.file.unzip_file",