gweb: Make sure to destroy the lookup before calling any result function

gweb: Make sure to destroy the lookup before calling any result function

Program received signal SIGSEGV, Segmentation fault.
Backtrace:
0  0x00000000004219fe in _debug (resolv=0x75f9a0, file=0x497267 "gweb/gresolv.c",
    caller=0x497598 "destroy_lookup",
    format=0x497278 "lookup %p id %d ipv4 %p ipv6 %p") at gweb/gresolv.c:136
1  0x0000000000421ac5 in destroy_lookup (lookup=0x760e40) at gweb/gresolv.c:154
2  0x00000000004224ce in sort_and_return_results (lookup=0x760e40) at gweb/gresolv.c:520
3  0x0000000000422597 in query_timeout (user_data=0x760510) at gweb/gresolv.c:542
4  0x00007ffff7b1b26b in g_timeout_dispatch (source=0x760ea0, callback=<optimized out>,
    user_data=<optimized out>) at gmain.c:4095
5  0x00007ffff7b1a643 in g_main_dispatch (context=0x6f5110) at gmain.c:2784
6  g_main_context_dispatch (context=0x6f5110) at gmain.c:3288
7  0x00007ffff7b1a988 in g_main_context_iterate (dispatch=1, block=<optimized out>,
    context=0x6f5110, self=<optimized out>) at gmain.c:3359
8  g_main_context_iterate (context=0x6f5110, block=<optimized out>, dispatch=1,
    self=<optimized out>) at gmain.c:3296
9  0x00007ffff7b1ade5 in g_main_loop_run (loop=0x6f4fe0) at gmain.c:3553
10 0x0000000000442a5f in main (argc=1, argv=0x7fffffffdea8) at src/main.c:705

Reported by Daniel Wagner