segfaults

Hi!

I love mmproxy, it helps me a lot hiding my SSH server behind a HA proxy. Unfortunately, multiple times a day the mmproxy process crashes with a segfault.

I have no experience reporting segfaults, this is my first report :) ... so I send you the information I think you need - please ask for further information, if needed:

OS: CentOS 7.5.1804
Kernel: 3.10.0-862.el7.x86_64

Log lines:
```
Feb 24 03:41:28 server kernel: [10342272.180498] mmproxy[59252]: segfault at 2b3e510 ip 0000000000444934 sp 00007fff29837dd0 error 4 in mmproxy[400000+fd000]
Feb 24 03:41:39 server kernel: [10342283.488181] mmproxy[17168]: segfault at 12bc510 ip 0000000000444934 sp 00007fff93723c00 error 4 in mmproxy[400000+fd000]
Feb 24 03:43:32 server kernel: [10342395.810838] mmproxy[17218]: segfault at 135e510 ip 0000000000444934 sp 00007fff070719e0 error 4 in mmproxy[400000+fd000]
Feb 24 03:43:42 server kernel: [10342406.580925] mmproxy[17583]: segfault at 2902510 ip 0000000000444934 sp 00007ffc2cd3c780 error 4 in mmproxy[400000+fd000]
```

Any thoughts on that?

Thank you for that great piece of software!