You are probably very new to working in IT/programming if this shocks you and a clause like this is new to you.
I would ask myself how much a regular salary is worth over the value of a "maybe" idea you are not committed to already.
My personal advice is spend your time and energy honing your skills to increase your leverage with employers. When you are ready to take an idea to market you'll need to understand how businesses work, etc. You can learn that at work. Pay attention to everything.