Handle case where function caller is null

Author: bengourley

stack-generator.js

@@ -22,6 +22,9 @@
 
             var curr = arguments.callee;
             while (curr && stack.length < maxStackSize) {
+                if (!curr['arguments']) {
+                  break;
+                }
                 // Allow V8 optimizations
                 var args = new Array(curr['arguments'].length);
                 for (var i = 0; i < args.length; ++i) {