Optimize allowList matching

If `allowList` is empty, theres no need to check `matchFound` because it's always true.
Also, if a match was found, theres no need to check the remaining entries.
Actually, I think this can be further simplified.

```
	if len(p.allowList) > 0 {
		for _, rgx := range p.allowList {
			if rgx.MatchString(u.Host) {
				http.Error(w, "Allowlist host failure", http.StatusNotFound)
				return
			}
		}
	}
```

I can either merge what you have and fix it after, or you could change it and then I can merge. 
Thanks for the changes!