In p2p code, iterator is not robust to concurrent modification in _handle_message_calls_in_progress loop

[vikramrajkumar]

From @theoreticalbts on February 25, 2016 16:3

The problem is here. The code walks an std::list using an iterator, but the cancel_and_wait() call allows other FC tasks to run, some of which modify the list and invalidate the iterator.

Copied from original issue: cryptonomex/graphene#598