I don't consider the HBOgo map a spoiler. Every fantasy novel I remember had maps in the front of the book. Plus I think that map only designates areas that have been mentioned, with some unmentioned geographical landmarks.

Anyways, Qarth is on a peninsula and a narrow channel. This means the "Sea of Bones" or what Jorah called the land around Qarth would not exist. There would be great activity all along the coastline, and even if there wasn't, wanderers would still contact enough wildlife and food to not default die if Qarth shuts its doors to them.

Geographically, GRRM uses way too much sea/water access for them to have such small navies and mobility. The food sources and travel logistics seem all sorts of messed up too.