Call rrdp_data_handler() for any kind of poll event that has happened.

Call rrdp_data_handler() for any kind of poll event that has happened.
On OpenBSD closing a connection will result in a read even (POLLIN) while
on Linux POLLHUP is returned. rrdp_data_handler()'s read() call returns
in both cases 0 and finishes the XML parsing.
Found and fix tested by job@, OK deraadt@