[sr-dev] segfault when trying to give xlog an expression param

[Juha Heinanen]

i tried to give xlog an expression param and got segfault at startup:

Apr 22 14:29:41 sip kernel: [53028.559446] sip-proxy[8339]: segfault at f30cbd8b ip 080c7616 sp bfa74da0 error 5 in sip-proxy[8048000+18e000]
Not starting sip-proxy: invalid configuration file!

 0(8339) INFO: pv [pv_shv.c:61]: locks array size 16
 0(8339) : <core> [cfg.y:3437]: parse error in config file /etc/sip-proxy/sip-proxy.cfg, line 1531, column 24-58: function xlog: parameter 2 is not constant

it would be better to just to give the error message without
segfaulting.  this was with master branch.

-- juha