fix segfault in blobdeport

[alexvru]

https://nda.ya.ru/t/j2tWMDfM7Cy3GW

0std::__y1::__function::__func<NKikimr::NBlobDepot::TBlobDepot::TData::StartLoad()::$_0, std::__y1::allocator<NKikimr::NBlobDepot::TBlobDepot::TData::StartLoad()::$_0>, void ()>::operator()() () contrib/ydb/core/blob_depot/coro_tx.cpp +182
1NKikimr::NBlobDepot::TCoroTx::TContext::DoRun() () contrib/libs/cxxsupp/libcxx/include/__functional/function.h +519
2ITrampoLine::DoRunNaked() () util/system/context.cpp +38

More details are in startrack

https://st.yandex-team.ru/KIKIMR-22740