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ARM64: Fix IR_SLOAD assembly.

Reported by Gate88.

(cherry picked from commit 6c4826f12)

The issue is in the case when IR SLOAD is unused on a trace, persists
only for typecheck, and has the `num` type. In this case, the `dest`
register is `RID_NONE`. Hence, the `fmov` instruction is emitted
unconditionally, where the destination register is `d0` (`RID_NONE &
31`). So, the value of this register is spoiled. If it holds any value
evaluated before and used after this SLOAD, it leads to incorrect
behaviour.

This patch adds the check that the register is in use before emitting
the instruction.

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

Part of tarantool/tarantool#11278

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