try/catch in HandleOKCallback

[springmeyer]

We should add try/catch around code in the HandleOKCallback like

node-cpp-skel/src/object_async/hello_async.cpp

Lines 179 to 186 in c3d13e7

	Nan::HandleScope scope;
	const auto argc = 2u;
	v8::Local<v8::Value> argv[argc] = {
	Nan::Null(), Nan::New<v8::String>(result_).ToLocalChecked()};
	// Static cast done here to avoid 'cppcoreguidelines-pro-bounds-array-to-pointer-decay' warning with clang-tidy
	callback->Call(argc, static_cast<v8::Local<v8::Value>*>(argv));

. Otherwise down stream developers are likely to:

• add new code to the HandleOKCallback
• in many instances that code might throw
• a throw will not be caught automatically and will instead crash the process with an abort

An example is mapbox/vtquery#69 /cc @mapsam

We must protect against crashes like this, so I think its worth adding try/catch around the code in node-cpp-skel. Then users would be forced (due to the lack of coverage of the catch to think hard about whether an exception is possible.