Fix matchSubdomain function to correctly handle exact domain matches

[suwakei]

Problem

The matchSubdomain function incorrectly returns false for exact domain matches without wildcards—for example, http://example.com vs. http://example.com.

Cause

Even if all parts match during iteration, the function still returns false at the end.

Fix

After the loop, if all parts match and the number of parts is equal between the pattern and the domain, it should return true—i.e., treat it as an exact match.

This PR adds that check.

[suwakei]

Hi! Just following up to see if there's anything I can improve in this PR 🙇

[FrancoTampieri]

My two cents:
I think the only think is missed the specific test for that case in util_test.go

[suwakei]

I added specific unit test