Fix self-assign evaluation order for ASSIGN_DIM_OP

For $ary[idx] op= $ary we should evaluate the RHS operand first,
otherwise we may create a reference-free recursive array. Use the

Fix self-assign evaluation order for ASSIGN_DIM_OP

For $ary[idx] op= $ary we should evaluate the RHS operand first,
otherwise we may create a reference-free recursive array. Use the
same handling we do for the normal $ary[idx] = $ary case.

Fixes oss-fuzz #40287.

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