Fix segfault if .clone is called with this==undefined

Author: gfwilliams

ChangeLog

@@ -26,6 +26,7 @@
             ESP32: update EspruinoBuildTools to esp-idf V3.1.3
             nRF52: Add FAT Filesystem support to MDBT42Q module
             Now save file modification time with FAT
+            Fix segfault if `.clone` is called with `this==undefined`
 
      2v01 : ESP32: update to esp-idf V3.1
             Fix issues with Class Extends

src/jswrap_object.c

@@ -142,6 +142,7 @@ JsVar *jswrap_object_toString(JsVar *parent, JsVar *arg0) {
 Copy this object completely
  */
 JsVar *jswrap_object_clone(JsVar *parent) {
+  if (!parent) return 0;
   return jsvCopy(parent, true);
 }