When constraint system has forks in it usually we solve all of them before
starting full completion of corresponding call. But if some call with
forks was a last statement of postponed lambda, we will never call
completion for it with FULL mode. Instead of it we complete it in PARTIAL
mode and then just merge its constraint storage into storage of outer
call. So all forks from this inner call just remain unresolved inside
outer system without this fix
^KT-55966 Fixed
Dmitriy Novozhilov