src: keep reference buffer alive longer

Keep a buffer written by WritePointer alive
until the finalizers for the buffer to which
the pointer has been run have been executed:

Refs: #54

Signed-off-by: Michael Dawson <mdawson@devrus.com>

src/binding.cc

@@ -355,6 +355,16 @@ void WritePointer(const CallbackInfo& args) {
   if (input.IsNull()) {
     *reinterpret_cast<char**>(ptr) = nullptr;
   } else {
+    // create a node-api reference and finalizer to ensure that
+    // the buffer whoes pointer is written can only be
+    // collected after the finalizers for the buffer
+    // to which the pointer was written have already run
+    Reference<Value>* ref = new Reference<Value>;
+    *ref = Persistent(args[2]);
+    args[0].As<Object>().AddFinalizer([](Env env, Reference<Value>* ref) {
+      delete ref;
+    }, ref);
+
     char* input_ptr = GetBufferData(input);
     *reinterpret_cast<char**>(ptr) = input_ptr;
   }