xl2tpd-1.3.6+dfsg-2build1 periodically crashes if compiled with USE_KERNEL

Ubuntu 15.04 x86_64

xl2tpd-1.3.6+dfsg-2build1 compiled from Ubuntu-supplied sources with adding OSFLAGS+= -DUSE_KERNEL to the Makefile

xl2pd daemon works very well and really uses kernel, so CPU usage is very low on my 450 Mbits-limited ISP uplink using L2TP

however, once in a day, randomly, xl2tpd crashes like this
xl2tpd[2414]: segfault at 188 ip 000000000040c7f8 sp 00007fffb1345280 error 4 in xl2tpd[400000+1c000]
wih dead ppp0 interface present but not working, staying for 2-3 min, then disappearing

looking into the code at the crash point reveals this in call.c line 416
---
#ifdef IP_ALLOCATION
    if (c->addr)
        unreserve_addr (c->addr);

    if (c->lns->localrange) // <-- this is the crash location
        unreserve_addr (c->lns->localaddr);
#endif
---

clearly c->lns is null pointer, so I patched this source a little:
---
    if (c->lns && c->lns->localrange)
        unreserve_addr (c->lns->localaddr);
---

compiled, installed and 1 week no crashes, no memory leaks and stable L2TP tunnel

this code introduced in patch 0003-Add-local-ip-range-option.patch and seems xl2tpd-1.3.6+dfsg-3 have same issue, the code of call.c is the same

seems problem exists in debian too
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=760602

please consider a quick fix. thanks.