Fix console warning including 'undefined' and a type violation

[michaelboyles]

This fixes the following console warning including 'undefined', if the user never specifies that config option

console.warn(`Max reconnect attempts of ${optionsRef.current.reconnectAttempts} exceeded`);

There's another instance of the same warning which null-coalesces the default of 20 before printing, which is more sensible.

It also fixes this typecast being wrong. optionsRef.current.reconnectAttempts is possibly undefined, and onReconnectStop is not declared to accept that (hence the cast, I guess).

optionsRef.current.onReconnectStop && optionsRef.current.onReconnectStop(optionsRef.current.reconnectAttempts as number);

After I'd changed that, my IDE warned me that reconnect section was an exact duplicate. I don't always pay attention to that warning, but since there were 2 functions doing the same thing, one with bugs and one without, it seemed a good candidate to extract to new a function so that they don't diverge again.

This change is split into 2 commits: the functional change to fix the bugs, then the refactor.

@robtaussig Please review!