Exact Riemann solver can get stuck in infinite loop

Just stumbled upon this issue. There is a while loop in riemann_solve_brent that has no emergency exit if it doesn't converge, and I got into a situation where that was the case, and the code was stuck in an infinite loop.

This needs fixing, but I'm not sure what the best approach to exception-handle that is. @yuyttenhove , do you have some experience with the brent method for the exact Riemann solver? Could you perhaps look into this?