box: fix segfault in box.internal.compact

There is an internal Lua function `box.internal.compact` that used in
`index_object:compact()` [1]. Tarantool has crashed when
`box.internal.compact` running with id of non-existent space.

Patch adds spaces cache initialization to box_init() and removes
excessive check in space_cache_destroy().

1. https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_index/compact/

Fixes #8196

NO_DOC=bugfix for internal Lua function
NO_CHANGELOG=bugfix for internal Lua function