fix(lib) prevent a segfault loading an empty .wat module with V8

[thibaultcha]

Fix #543

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.05848%. Comparing base (91d447f) to head (55b5481).

Additional details and impacted files

[](https://app.codecov.io/gh/Kong/ngx_wasm_module/pull/544?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Kong) ```diff @@ Coverage Diff @@ ## main #544 +/- ## ============================================= Coverage 90.05848% 90.05848% ============================================= Files 47 47 Lines 10089 10089 ============================================= Hits 9086 9086 Misses 1003 1003 ``` | [Flag](https://app.codecov.io/gh/Kong/ngx_wasm_module/pull/544/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Kong) | Coverage Δ | | |---|---|---| | [unit](https://app.codecov.io/gh/Kong/ngx_wasm_module/pull/544/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Kong) | `90.15117% <ø> (ø)` | | | [valgrind](https://app.codecov.io/gh/Kong/ngx_wasm_module/pull/544/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Kong) | `78.01542% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Kong#carryforward-flags-in-the-pull-request-comment) to find out more.