Fix crash in shell.cc when reporting exceptions that aren't Errors

samples/shell.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 394 matching lines @@
     // Print wavy underline (GetUnderline is deprecated).
     int start = message->GetStartColumn(context).FromJust();
     for (int i = 0; i < start; i++) {
       fprintf(stderr, " ");
     }
     int end = message->GetEndColumn(context).FromJust();
     for (int i = start; i < end; i++) {
       fprintf(stderr, "^");
     }
     fprintf(stderr, "\n");
-    v8::String::Utf8Value stack_trace(
-        try_catch->StackTrace(context).ToLocalChecked());
-    if (stack_trace.length() > 0) {
-      const char* stack_trace_string = ToCString(stack_trace);
-      fprintf(stderr, "%s\n", stack_trace_string);
+    v8::Local<v8::Value> stack_trace_string;
+    if (try_catch->StackTrace(context).ToLocal(&stack_trace_string) &&
+        stack_trace_string->IsString()) {
+      v8::String::Utf8Value stack_trace(stack_trace_string);
+      if (stack_trace.length() > 0) {

[vogelheim, 2015/10/20 12:59:47]

nitpick: Since you're checking stack_trace_string validity in the previous if,
you could merge this check into the if above.

(Assuming there's no way that you'd have a valid, non-empty v8::String that
somehow turns into a zero-length Utf8Value.)

+        const char* stack_trace_string = ToCString(stack_trace);
+        fprintf(stderr, "%s\n", stack_trace_string);
+      }
     }
   }
 }