Logically to me, sugar water, or any food for that matter, can only spoil if there is bacteria/fungus available to make it begin to break down. Thinking on fermenting (as would be the fear with sugar water), that requires yeast, wild or cultured. If you sterilize and pasteurize you should be OK. I was just thinking about mixing up a bunch and pressure canning it, but the time that would go into all that just so I could grab a quart jar from time to time is not worth it. I just keep a bag of sugar ready in a pinch and use hot tap water to mix it quickly. Normally I plan it better and mix a 5 gallon batch and put it all out, as I always have a few nucs with jars and a few struggling colonies that I can give it to.