Remove file_error() calls after pcap_read_block() calls.

pcap_read_block() takes err and err_info arguments, and sets them on
error; no need to call file_error() if pcap_read_block() fails.

Change-Id: I33b96d31395bf7d66abdecbebd5cf775e8662004
Reviewed-on: https://code.wireshark.org/review/4209
Reviewed-by: Guy Harris <guy@alum.mit.edu>