Under load changing shard mode can lead to it being removed from the
list during some other PUT.
```
Dec 28 07:01:26 az neofs-node[364505]: panic: runtime error: invalid memory address or nil pointer dereference
Dec 28 07:01:26 az neofs-node[364505]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0xc9fbb1]
Dec 28 07:01:26 az neofs-node[364505]: goroutine 11791912 [running]:
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.(*StorageEngine).putToShard(0xc000435490, {0xc0003f7a28?, 0xc0001192c0?}, 0x2, {0x0, 0x>
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/put.go:91 +0x1b1
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.(*StorageEngine).put.func1(0xc000435490?, {0xc0003f7a28?, 0xc0001192c0?})
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/put.go:71 +0x19c
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.(*StorageEngine).iterateOverSortedShards(0x1?, {{0x62, 0x23, 0xfe, 0x60, 0x67, 0xd5, 0x>
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/shards.go:225 +0xc8
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.(*StorageEngine).put(0xc000435490, {0x1?})
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/put.go:66 +0x2a9
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.(*StorageEngine).Put.func1()
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/put.go:43 +0x2a
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.(*StorageEngine).execIfNotBlocked(0x8?, 0x38?)
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/control.go:147 +0xcf
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.(*StorageEngine).Put(0xc4df775a80?, {0x0?})
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/put.go:42 +0x65
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine.Put(0xc06d928b80?, 0xc06b1b8dc8?)
Dec 28 07:01:26 az neofs-node[364505]: github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine/put.go:158 +0x19
Dec 28 07:01:26 az neofs-node[364505]: main.engineWithoutNotifications.Put({0x20301b?}, 0x20301b?)
```
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
Evgenii Stratonikov
ba393e3e91