Fix stack trace printing in d8

src/d8.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 // Defined when linking against shared lib on Windows.
 #if defined(USING_V8_SHARED) && !defined(V8_SHARED)
 #define V8_SHARED
 #endif
 
@@ skipping 899 matching lines @@
     for (int i = 0; i < start; i++) {
       printf(" ");
     }
     int end = message->GetEndColumn(isolate->GetCurrentContext()).FromJust();
     for (int i = start; i < end; i++) {
       printf("^");
     }
     printf("\n");
     Local<Value> stack_trace_string;
     if (try_catch->StackTrace(isolate->GetCurrentContext())
-            .ToLocal(&stack_trace_string)) {
+            .ToLocal(&stack_trace_string) &&
+        stack_trace_string->IsString()) {
       v8::String::Utf8Value stack_trace(
           Local<String>::Cast(stack_trace_string));
       printf("%s\n", ToCString(stack_trace));
     }
   }
   printf("\n");
 #ifndef V8_SHARED
   if (enter_context) utility_context->Exit();
 #endif  // !V8_SHARED
 }
@@ skipping 1674 matching lines @@
 }
 
 }  // namespace v8
 
 
 #ifndef GOOGLE3
 int main(int argc, char* argv[]) {
   return v8::Shell::Main(argc, argv);
 }
 #endif