Core: Fix filtering UNIT_* events by unitId

[oomshroom]

Fix filtering by unit in UNIT_* events.
Fixes event filters such as "UNIT_HEALTH boss1" not working at all.

[Zidras]

@oomshroom, can you briefly explain why this is needed? I'd have to check on some recent logs but I have no ticket open for unit health not working

[oomshroom]

@oomshroom, can you briefly explain why this is needed? I'd have to check on some recent logs but I have no ticket open for unit health not working

Currently all timers/warnings which use "UNIT_HEALTH boss1" are broken. These are mostly "Next Phase Soon"-style warnings, such as Deathbringer's Frenzy and Sindragosa's P2.
In practice UNIT_HEALTH is the only event affected, but it is a commonly used event.

In DBM:ADDON_LOADED(), DBM registers "UNIT_HEALTH mouseover target focus player" on the main frame. In the existing code, handleEvent(self, "UNIT_HEALTH", "boss1") checks the first entry in registeredEvents, which for UNIT_HEALTH is the DBM main frame, and immediately returns because boss1 is not wanted there. Other entries in registeredEvents, such as those from a boss mod, are never checked!

[Zidras]

@oomshroom, it is a valid issue, thanks for bringing this up and PR'ing a fix.
I will try to look into it during next week

[Zidras]

Merged at last! Thank you @oomshroom for your contribution