Prevent potential overflow

[Septa2112]

PR #4300 introduced the rationale for validating heap_type.

This patch moves the validation before the computation of type1 to prevent potential overflow.

[Septa2112]

Further improved the heap type check logic:

1. Moved the heap type validation ahead of the if (!is_byte_a_type...) check. Depending on whether heap_type >= 0, different methods are used to get type1.

2. The type_index check is now performed only when heap_type >= 0, to ensure that type1 is correctly retrieved in this case.

3. Why not checking type_index when heap_type < 0? Because in the current WAMR implementation, if wasm_is_valid_heap_type(heap_type) is true, then the condition if (!is_byte_a_type(type1) || wasm_is_type_multi_byte_type(type1)) will always be false.

[lum1n0us]

better have a comment @l867 to hint that if heap_type < 0, if (!is_byte_a_type(type1) || wasm_is_type_multi_byte_type(type1)) will be false.

[lum1n0us]

Another suggestion is to merge those if...else.. blocks, like:

if (heap_type >= 0) {
    if (!check_type_index(module, module->type_count, heap_type,
                          error_buf, error_buf_size)) {
        goto fail;
    }
    wasm_set_refheaptype_typeidx(&cur_ref_type.ref_ht_typeidx,
                                 true, heap_type);
    if (!push_const_expr_stack(&const_expr_ctx, flag,
                               cur_ref_type.ref_type,
                               &cur_ref_type, 0, &cur_value,
                               error_buf, error_buf_size))
        goto fail;

}
else {
    if (!wasm_is_valid_heap_type(heap_type)) {
        set_error_buf_v(error_buf, error_buf_size,
                        "unknown type %d", heap_type);
        goto fail;
    }
    type1 = (uint8)((int32)0x80 + heap_type);
    if (!push_const_expr_stack(&const_expr_ctx, flag, type1,
                               NULL, 0, &cur_value, error_buf,
                               error_buf_size))
        goto fail;
}