Fix pcap_offline_read() loop.

Fix pcap_offline_read() loop.

It should loop until either

	1) we get an error reading packets, but we already do that;

	2) we get an EOF reading packets, but we already do that;

	3) we return the number of packets the caller asked for (if they
	   asked for a given number), but we already do that;

so there's no need for the loop condition to check the status - and the
old test didn't work, as the meaning of the status returned by the
next_packet_op routine changed.

(cherry picked from commit 292ce0079b21df0dc34233e1b094a556d6b84753)