Fix reource registraton error 500 on empty or bad ptr file

pandora_console/extensions/resource_registration.php

@@ -1096,8 +1096,13 @@ function resource_registration_extension_main()
     }
 
     $xml = simplexml_load_file($_FILES['resource_upload']['tmp_name'], null, LIBXML_NOCDATA);
-
-    process_upload_xml($xml);
+    if ($xml === false) {
+        ui_print_error_message(
+            __('Error uploading resource. Check if the selected file is a valid resource template in .ptr format')
+        );
+    } else {
+        process_upload_xml($xml);
+    }
 }