remove unset of array key that explicitly does not exist

[borbyu]

depending on notice level, this could cause errors

[tocker]

Hi @borbyu ,

Thanks for the PR!
In option_consume, the key may exist with NULL value. Thus unset($options[$option]) is required even if isset returned false.
It would be more accurate to use array_key_exists instead of isset. However inset is much more efficient than array_key_exists - about 5 times as fast!