Segmentation fault if operating on a closed sniffer

[dainok]

Tested on:

• Python 3.6.4
• both Linux and MacOS (same behaviour)
• pypcap 1.2.2

Steps to reproduce:

import pcap
a = pcap.pcap()
a.close()
a.close()
Segmentation fault: 11

I think that pypcap should raise an exception, avoiding a segmentation fault.

[hellais]

Yes this seems like a bug. We should at least raise an exception and keep track of the opened state in python or ideally fix it in the underlying c code.