filter-aaaa crash in 9.14.1

still happends on 9.14.1 with the patch from issue 982

(gdb) bt

#0 0x00000033772324f5 in raise () from /lib64/libc.so.6

#1 0x0000003377233cd5 in abort () from /lib64/libc.so.6

#2 0x000000000041e3d3 in assertion_failed (file=, line=, type=, cond=) at ./main.c:253

#3 0x0000003fb421323a in isc_assertion_failed (file=, line=, type=, cond=) at assertions.c:50

#4 (closed) 0x0000003fb42184b0 in isc_ht_destroy (htp=0x7f548e8db628) at ht.c:114

#5 (closed) 0x00007f547ad1fa8c in plugin_destroy (instp=0x7f5483118698) at filter-aaaa.c:450

#6 (closed) 0x0000003fb4616462 in unload_plugin (pluginp=) at hooks.c:238

#7 (closed) 0x0000003fb461657a in ns_plugins_free (mctx=0x1e24210, listp=) at hooks.c:553

#8 (closed) 0x0000003fb3d51945 in destroy (view=0x7f547c2bcf50) at view.c:557

#9 (closed) 0x0000003fb3d5222c in adb_shutdown (task=, event=0x0) at view.c:762

#10 (closed) 0x0000003fb4233b17 in dispatch (queuep=) at task.c:1130

#11 (closed) run (queuep=) at task.c:1297

#12 (closed) 0x0000003377e07aa1 in start_thread () from /lib64/libpthread.so.0

#13 (closed) 0x00000033772e8c4d in clone () from /lib64/libc.so.6