Avoid invalidating pointer

[siddhesh]

Decrementing io when it is at the start of the object sends it out of bounds, thus invoking undefined behaviour. Always increment the pointer instead.

Resolves: #78

[jakubjelinek]

IMHO if you do this (which LGTM), then you should also do the same thing with step increments/decrements,
as there is just one spot where you want to increment it and one spot where you don't, moving it from for increment
expression to before continue and removing the decrement is better.

[siddhesh]

IMHO if you do this (which LGTM), then you should also do the same thing with step increments/decrements, as there is just one spot where you want to increment it and one spot where you don't, moving it from for increment expression to before continue and removing the decrement is better.

Done, thanks.

[dk]

@ppisar could you confirm that this doesn't coredump on your setup?

[dk]

Thank you Siddhesh

[ppisar]

I confirm this commit fixes the abort on my system.