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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 to optimistic JIT maxslot.
In that case, the slot above the top of the Lua stack may be considered
as used. When any VM event handler is called before the recording of the
next instruction, this leads to the assertion failure in the
`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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