Fix logic error in roots.hpp

[jzmaddock]

Fixes #776

[TFiFiE]

This fix is itself somewhat problematic insofar that one can no longer reliably test whether the algorithm hit the iteration limit just by checking if the function changed max_iter. It can now also have been decremented by one.

[jzmaddock]

This fix is itself somewhat problematic insofar that one can no longer reliably test whether the algorithm hit the iteration limit just by checking if the function changed max_iter. It can now also have been decremented by one.

I don't follow - the main loop will still decrement max_iter, the change is that now, if there are insufficient iterations left, then we just don't try the alternate bracketing algorithm.

[TFiFiE]

Before, max_iter didn't get decremented if it ended up being responsible for stopping the algorithm, because count was guaranteed to be decremented at least once in bracket_root_towards_min and bracket_root_towards_max. Although this change might technically be correct, it is now no longer the case that max_iter being changed necessarily implies that it had no hand in stopping the algorithm.