IIS: fix dead Host header fallback (r->hostname == NULL can never be true)

[A13501350]

Summary

Fixes the Host header fallback being dead code in the IIS module.

r->hostname is set from ConvertUTF16ToUTF8(req->CookedUrl.pHost, ...) (line 840). That helper never returns NULL — on NULL/empty input, zero converted bytes, or conversion failure it returns the literal "" (mymodule.cpp:180-184, :199-202, :226-229); on success it returns a pool-allocated buffer. So r->hostname is always non-NULL, and if(r->hostname == NULL) at line 843 was never true, silently skipping the Host header fallback.

Now the check also triggers on an empty string, so when the request URI carries no host (ordinary HTTP/1.1 GET /path + Host: header) the host is taken from the Host header as intended.

Fixes

Closes #3621

Changed location

• iis/mymodule.cpp:843 — if(r->hostname == NULL) → if(r->hostname == NULL || r->hostname[0] == '\0')

The helper's contract is intentionally left unchanged so the other callers (path_info, args) are unaffected.

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[sonarqubecloud]

Quality Gate failed

Failed conditions
E Maintainability Rating on New Code (required ≥ A)

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