Merge uws.webserver_has_event with uws.webserver_get_next_event to eliminate useless function calls

[rdw-software]

The docs for uws.webserver_get_next_event state:

This seems like a minor issue with the design: Why can't the bindings just return false in this case (no copying), and true otherwise? Currently, the return type is void and this is done via webserver_has_event instead. Both of these can be merged.

The difference will likely be minor and I'd bet that LuaJIT can optimize this away, but removing a function would simplify the API.

TBD:

• Is there ever a use case where you want to check that there are events in the buffer without fetching them afterwards?
• Isn't webserver_get_event_count sufficient enough to check that there are events? Seems a bit redundant, if less clear

Since these are FFI bindings and not high-level APIs, simplifying the API surface should be more valuable than clarity of intent.