[Bug Fix] Fix stack leaks in Lua events

[hgtw]

EventItem was leaving the package table on the stack in successful
(non-encounter) calls and only popping the return. All events were
also leaking the full stack on lua_pcall errors. Lua mod callbacks
were popping error returns but leaking the table.

[Quintinon]

Is there a different coding pattern or some generic checks that could be put in place to prevent this from happening again?

[hgtw]

Avoiding returns in the middle of functions and using lua_settop(L, 0) to clear the stacks instead of popping tracked counts. I didn't want to add noise (and more testing) to this by refactoring things though