comms/hylafax: Fix build with Clang 6 (and GCC7)

Add patch from upstream HylaFAX+, fixing a Clang 6 (and GCC7) build error:

FaxRecvInfo.c++:115:17: error: comparison between pointer and integer ('const char *' and 'int')

while (cp+2 != '\0') {
       ~~~~ ^  ~~~~

[1] http://bugs.hylafax.org/show_bug.cgi?id=971
[2] https://sourceforge.net/p/hylafax/HylaFAX+/2417/
[3] See Also: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=853448

PR: 225372
Reported by: O. Hartmann <ohartmann walstatt org>
Obtained from: HylaFAX+ [2]
MFH: 2018Q4