Confusion regarding garlic powder in fat in pan
This site suggests that when commercial garlic powder is made it is heated to a temperature of 150 to 160 degrees Celsius, before it is then dehydrated and ground.  C. Botulinum spores are killed by heating to at least 120 degrees Celcius, and holding for at least 30 minutes. It would seem to me that commercial producers of garlic powder would certainly want to take care of this potential hazard.  If you were using commercially made garlic powder, the chances that any C. Botulinum spores were present when you started are pretty slim.

Of course, if you made your own garlic powder, the risk is higher.  Also, keep in mind refrigeration, does not eliminate risk, but slows the growth of bacteria dramatically.