I wouldn' worry about it. It's only 1/2 charge anyway. Even if it ignites, it would probably be 1 particle at a time since they wouldn't stay together in a vacuum.
Have you ever noticed when you burn powder that just touching a match to it doesn't ignite it. It takes a second or two. The temp needs to be pretty high to ignite it. The lint in your vacuum is far more flammable than the gun powder.
If you're concerned, just empty the vacuum cleaner directly into the trash when you're done.