Guard against NULL returned by uv_err_name.

The uv_err_name would return NULL on unknown system error, which then would
crash V8 by creating string from NULL.

Author: zcbenz

src/node.cc

@@ -818,7 +818,11 @@ Local<Value> UVException(Isolate* isolate,
   if (!msg || !msg[0])
     msg = uv_strerror(errorno);
 
-  Local<String> js_code = OneByteString(isolate, uv_err_name(errorno));
+  const char* err_name = uv_err_name(errorno);
+  if (err_name == NULL)
+    err_name = "UnknownSystemError";
+
+  Local<String> js_code = OneByteString(isolate, err_name);
   Local<String> js_syscall = OneByteString(isolate, syscall);
   Local<String> js_path;
   Local<String> js_dest;

src/uv.cc

@@ -22,6 +22,8 @@ void ErrName(const FunctionCallbackInfo<Value>& args) {
   if (err >= 0)
     return env->ThrowError("err >= 0");
   const char* name = uv_err_name(err);
+  if (name == NULL)
+    name = "UnknownSystemError";
   args.GetReturnValue().Set(OneByteString(env->isolate(), name));
 }