Comment 15 for bug 1961442

Core dump is attached and backtrace is;
```
Thread 1 "NetworkManager" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 13139.13139]
0x00007f08b4e885f4 in g_str_hash () from target:/lib/x86_64-linux-gnu/libglib-2.0.so.0
(gdb) bt
#0 0x00007f08b4e885f4 in g_str_hash () from target:/lib/x86_64-linux-gnu/libglib-2.0.so.0
#1 0x00007f08b4e8773c in g_hash_table_lookup () from target:/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007f08b51d34cb in netplan_delete_connection () from target:/lib/x86_64-linux-gnu/libnetplan.so.0.0
#3 0x000055d2d91132f9 in delete_connection (plugin=0x55d2da712400, storage_x=<optimized out>, error=<optimized out>) at src/settings/plugins/keyfile/nms-keyfile-plugin.c:1029
#4 0x000055d2d910fe22 in nm_settings_delete_connection (self=0x55d2da6f4000, sett_conn=sett_conn@entry=0x55d2da6e4540, allow_add_to_no_auto_default=allow_add_to_no_auto_default@entry=0)
    at src/settings/nm-settings-storage.h:57
#5 0x000055d2d928aef1 in nm_settings_connection_delete (self=self@entry=0x55d2da6e4540, allow_add_to_no_auto_default=allow_add_to_no_auto_default@entry=0) at src/settings/nm-settings-connection.c:612
#6 0x000055d2d912d4b0 in _delete_volatile_connection_do (connection=0x55d2da6e4540, self=0x55d2da6f0010) at src/nm-manager.c:837
#7 _delete_volatile_connection_do (self=0x55d2da6f0010, connection=0x55d2da6e4540) at src/nm-manager.c:818
#8 0x000055d2d912d53b in _delete_volatile_connection_all (self=0x55d2da6f0010, do_delete=do_delete@entry=1) at src/nm-manager.c:2198
#9 0x000055d2d912d55c in _delete_volatile_connection_cb (user_data=<optimized out>) at src/nm-manager.c:2209
#10 0x00007f08b4e9a04e in g_main_context_dispatch () from target:/lib/x86_64-linux-gnu/libglib-2.0.so.0
#11 0x00007f08b4e9a400 in ?? () from target:/lib/x86_64-linux-gnu/libglib-2.0.so.0
#12 0x00007f08b4e9a6f3 in g_main_loop_run () from target:/lib/x86_64-linux-gnu/libglib-2.0.so.0
#13 0x000055d2d90fbd5a in main (argc=<optimized out>, argv=<optimized out>) at src/main.c:456
(gdb)
```