segfault when `modparam("presence", "subs_db_mode", 0)`
``` (gdb) (gdb) bt full #0 0x00007f12607da547 in atomic_cmpxchg_int (var=0x8, old=0, new_v=1) at ../../core/mem/../atomic/atomic_x86.h:224 ret = 32530 #1 0x00007f12607da57b in futex_get (lock=0x8) at ../../core/mem/../futexlock.h:99 v = 21864 i = 1024 #2 0x00007f12607fe0d0 in update_db_subs_timer_dbnone (no_lock=0) at subscribe.c:2079 i = 0 now = 1587487071 s = 0x0 prev_s = 0x0 del_s = 0x5568ae3160b0 __func__ = "update_db_subs_timer_dbnone" #3 0x00007f1260802121 in timer_db_update (ticks=61825161, param=0x0) at subscribe.c:2441 no_lock = 0 __func__ = "timer_db_update" #4 0x00005568ade05b2e in sr_wtimer_exec (ticks=61825161, param=0x0) at core/timer_proc.c:433 wt = 0x7f126821dae8 wn = 0x0 wp = 0x0 cs = 4 __func__ = "sr_wtimer_exec" #5 0x00005568ade04b58 in fork_sync_timer (child_id=-1, desc=0x5568ae01a3a1 "secondary timer", make_sock=1, f=0x5568ade057a8 <sr_wtimer_exec>, param=0x0, interval=1000) at core/timer_proc.c:267 pid = 0 ts1 = 989202582 ts2 = 1000 #6 0x00005568ade05ece in sr_wtimer_start () at core/timer_proc.c:459 __func__ = "sr_wtimer_start" #7 0x00005568adc05e24 in main_loop () at main.c:1452 i = 21864 pid = 6405 si = 0x0 si_desc = "H4\037h\022\177\000\000\b\201\026h\022\177\000\000\000\000\200\000\003\000\000\000`.\022h\022\177", '\000' <repeats 13 times>, "\004\000\000\000\000H9\037h\022\177\000\000\323u\000\256hU\000\000\200\243\001\225\375\177\000\000\207ыh\022\177\000\000`\243\001\225\375\177\000\000 \000\000\000\060\000\000\000p\243\001\225\375\177\000\000\260\242\001\225\375\177\000\000\323u\000\256hU\000\000Pw\037h\022\177\000" nrprocs = 0 woneinit = 21864 __func__ = "main_loop" #8 0x00005568adc123e7 in main (argc=9, argv=0x7ffd9501a8a8) at main.c:2845 cfg_stream = 0x5568b01ad010 c = -1 r = 0 ---Type <return> to continue, or q <return> to quit--- tmp = 0x7f126976e708 "" tmp_len = 0 port = 0 proto = 32765 ahost = 0x0 aport = 0 options = 0x5568adfd3918 ":f:cm:M:dVIhEeb:l:L:n:vKrRDTN:W:w:t:u:g:P:G:SQ:O:a:A:x:X:Y:" ret = -1 seed = 4119354055 rfd = 4 debug_save = 4 debug_flag = 1 dont_fork_cnt = 1 n_lst = 0x7f126976d948 <_rtld_global+2312> p = 0x7f1268907010 <handle_intel+144> "H\205\300uTD9t$\fA\215V\001v0A\211ָ\002" st = {st_dev = 18, st_ino = 63494, st_nlink = 2, st_mode = 16832, st_uid = 0, st_gid = 0, __pad0 = 0, st_rdev = 0, st_size = 60, st_blksize = 4096, st_blocks = 0, st_atim = {tv_sec = 1587484687, tv_nsec = 26720353}, st_mtim = { tv_sec = 1587486933, tv_nsec = 570847206}, st_ctim = {tv_sec = 1587486933, tv_nsec = 570847206}, __glibc_reserved = {0, 0, 0}} tbuf = "\330\331vi\022\177\000\000\220Q\342h\022\177\000\000H\331vi\022\177\000\000\370\250\001\225\375\177\000\000p\341vi\022\177\000\000\000\000\000\000\000\000\000\000@\320vi\022\177\000\000\224{Ui\022\177\000\000\001", '\000' <repeats 15 times>, "\350\244\001\225\375\177\000\000\360,\207h\022\177\000\000 \247\001\225\375\177\000\000\332\361Ui\022\177\000\000\300@\301h\022\177\000\000\327\352\224h\022\177\000\000\240K\342h\022\177\000\000\200\071\301h\022\177\000\000(\224\342h\022\177\000\000\000\020", '\000' <repeats 14 times>, "\310\344vi\022\177\000\000\000\000\000\000\000\000\000\000ؗTi\022\177\000\000\220\223Ti\022\177\000\000\200"... option_index = 0 long_options = {{name = 0x5568adfd5916 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x5568adfd10e9 "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x5568adfd591b "alias", has_arg = 1, flag = 0x0, val = 1024}, { name = 0x5568adfd5921 "subst", has_arg = 1, flag = 0x0, val = 1025}, {name = 0x5568adfd5927 "substdef", has_arg = 1, flag = 0x0, val = 1026}, {name = 0x5568adfd5930 "substdefs", has_arg = 1, flag = 0x0, val = 1027}, { name = 0x5568adfd593a "server-id", has_arg = 1, flag = 0x0, val = 1028}, {name = 0x5568adfd5944 "loadmodule", has_arg = 1, flag = 0x0, val = 1029}, {name = 0x5568adfd594f "modparam", has_arg = 1, flag = 0x0, val = 1030}, { name = 0x5568adfd5958 "log-engine", has_arg = 1, flag = 0x0, val = 1031}, {name = 0x0, has_arg = 0, flag = 0x0, val = 0}} __func__ = "main" (gdb)