Initialize test variables; avoid false warnings.

[anhu]

Fixes #7356

[devin-ai-integration]

🛟 Devin Lifeguard found 1 likely issues in this PR

• check-return-codes snippet: Check the declaration of wc_SetUnknownExtCallback; if it returns an int, add “ret = wc_SetUnknownExtCallback(...); if (ret != 0) return ret;”.

@anhu
please take a look at the above issues which Devin flagged. Devin will not fix these issues automatically.