timer callback on already destroyed resolver object

Looks like the timer wasn't stopped or was recreated or something 😄

This is 9.19 only

D:statistics:Core was generated by `/builds/isc-projects/bind9/bin/named/.libs/named -D statistics-ns2 -X named.loc'.
D:statistics:Program terminated with signal SIGABRT, Aborted.
D:statistics:#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
D:statistics:[Current thread is 1 (Thread 0x7f7c0ff7f700 (LWP 15583))]
D:statistics:#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
D:statistics:#1  0x00007f7c132ae859 in __GI_abort () at abort.c:79
D:statistics:#2  0x00005581b7426cfb in assertion_failed (file=<optimized out>, line=<optimized out>, type=isc_assertiontype_require, cond=0x7f7c13d50100 "((res) != ((void *)0) && ((const isc__magic_t *)(res))->magic == ((('R') << 24 | ('e') << 16 | ('s') << 8 | ('!'))))") at main.c:238
D:statistics:#3  0x00007f7c13dd63ed in isc_assertion_failed (file=file@entry=0x7f7c13d4f156 "resolver.c", line=line@entry=10736, type=type@entry=isc_assertiontype_require, cond=cond@entry=0x7f7c13d50100 "((res) != ((void *)0) && ((const isc__magic_t *)(res))->magic == ((('R') << 24 | ('e') << 16 | ('s') << 8 | ('!'))))") at assertions.c:49
D:statistics:#4  0x00007f7c13c95256 in dns_resolver_createfetch (res=<optimized out>, name=name@entry=0x7f7c10056180, type=type@entry=48, domain=domain@entry=0x0, nameservers=nameservers@entry=0x0, forwarders=forwarders@entry=0x0, client=0x0, id=0, options=32802, depth=0, qc=0x0, task=0x7f7c10078240, action=0x7f7c13cf8eae <keyfetch_done>, arg=0x7f7c10056180, rdataset=0x7f7c10056400, sigrdataset=0x7f7c10056470, fetchp=0x7f7c100564f0) at resolver.c:10772
D:statistics:#5  0x00007f7c13cefce7 in zone_refreshkeys (zone=zone@entry=0x7f7be2603000) at zone.c:11301
D:statistics:#6  0x00007f7c13d113fd in zone_maintenance (zone=0x7f7be2603000) at zone.c:11536
D:statistics:#7  0x00007f7c13d119aa in zone_timer (arg=<optimized out>) at zone.c:15206
D:statistics:#8  0x00007f7c13dfe870 in timer_cb (handle=<optimized out>) at timer.c:113
D:statistics:#9  0x00007f7c13770256 in uv.run_timers () from /lib/x86_64-linux-gnu/libuv.so.1
D:statistics:#10 0x00007f7c137737ba in uv_run () from /lib/x86_64-linux-gnu/libuv.so.1
D:statistics:#11 0x00007f7c13de9309 in loop_run (loop=loop@entry=0x7f7c106a52e0) at loop.c:266
D:statistics:#12 0x00007f7c13de9374 in loop_thread (arg=0x7f7c106a52e0) at loop.c:293
D:statistics:#13 0x00007f7c13e03065 in isc__trampoline_run (arg=0x5581b89f1410) at trampoline.c:198
D:statistics:#14 0x00007f7c13486609 in start_thread (arg=<optimized out>) at pthread_create.c:477
D:statistics:#15 0x00007f7c133ab133 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95