operators can't WHOIS some utf-8 nicknames

[slingamn]

Reported by bogdomania on freenode. Ordinary users can WHOIS one other by their utf-8 nicknames. However, operators have enhanced capabilities --- their WHOIS arguments are treated as nickmasks with wildcards --- and something in this pipeline (maybe strings.Split, maybe ircmatch) fails to match certain utf-8 nicknames.

Reproduction steps:

1. Client 1 joins with a Hebrew nickname, e.g., ברוך
2. Client 2 joins and becomes an operator
3. Client 2 issues WHOIS ברוך
4. Client 2 receives, e.g., :oragono.test 401 פינחס ברוך :No such nick

[slingamn]

Came up again on #568

[slingamn]

Easy fix: if ircmatch doesn't find anything, just attempt to match as a simple nickname (like in the non-oper case).

[slingamn]

Oddly enough, this doesn't seem to affect KLINE, even though KLINE uses ircmatch as well? Maybe I'm testing the wrong cases?