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Fix maxslots when recording BC_TSETM.

Analyzed by Sergey Kaplun.

(cherry-picked from commit 0cc5fdfbc)

Recording of the `BC_TSETM` bytecode may keep the JIT maxslot too
optimistic. In that case, the slot above the top of the Lua stack may be
considered used. When any VM event handler is called before the
recording of the next instruction, this leads to an assertion failure in
`rec_check_slots()`.

This patch sets the `ra` as a maxslot, as far as the `ra` - 1 contains a
table, which is always the highest slot after this bytecode. Also, it
adds an assertion that we check slots below the top of the Lua stack.

Sergey Kaplun:
* added the description and the test for the problem

Part of tarantool/tarantool#8825

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