fix defer variable corruption

[rajashekar007]

As deferements are iterated using range based loop, when there is a recursive defer, it's corrupting the variable. The loop iteration has been changed to use index based to fix the same.

Kindly review it.

[AzothAmmo]

This strikes me as likely an incorrect usage of cereal::defer - it shouldn't be used in situations where there is any recursive structure to serialize as this defeats the purpose of the deferment in the first place.