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

samples/shell.cc

Index: samples/shell.cc
diff --git a/samples/shell.cc b/samples/shell.cc
index ad2228508439f6d14283d47bbb5b9e05519a6295..17b5767c62c8b9b5e2a53f0ad4c0921a7c6779b8 100644
--- a/samples/shell.cc
+++ b/samples/shell.cc
@@ -412,11 +412,14 @@ void ReportException(v8::Isolate* isolate, v8::TryCatch* try_catch) {
       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);
+      }
     }
   }
 }