ASSERT decode-stress translate.c:1094

This showed up on Windows 32-bit:

https://github.com/DynamoRIO/dynamorio/pull/4722/checks?check_run_id=1846725471
```
2021-02-06T23:18:34.8554457Z 32: Test command: /home/runner/work/dynamorio/dynamorio/build_debug-internal-32/bin32/drrun "-s" "90" "-quiet" "-debug" "-killpg" "-stderr_mask" "0xC" "-dumpcore_mask" "0" "-code_api" "--" "/home/runner/work/dynamorio/dynamorio/build_debug-internal-32/suite/tests/bin/linux.execve-rec"
2021-02-06T23:18:34.8555892Z 32: Test timeout computed to be: 600
2021-02-06T23:18:34.8556319Z 13: Start
2021-02-06T23:18:34.8556816Z 13: Jumping to a sequence of every addr16 modrm byte
2021-02-06T23:18:34.8557360Z 32: under DynamoRIO
2021-02-06T23:18:34.8557728Z 32: Sum(10)
2021-02-06T23:18:34.8558229Z 32: under DynamoRIO
2021-02-06T23:18:34.8558623Z 32: under DynamoRIO
2021-02-06T23:18:34.8559151Z 32: under DynamoRIO
2021-02-06T23:18:34.8559559Z 32: under DynamoRIO
2021-02-06T23:18:34.8561218Z 13:
2021-02-06T23:18:34.8573488Z 33/346 Test #13: code_api|common.decode-stress ....................................***Failed
```

Wow, and it showed up on Linux x86-64:
https://github.com/DynamoRIO/dynamorio/pull/4722/checks?check_run_id=1846725471