Buffer errors in case of 2 and more clients

[maxim-sheronov]

DollController starts call _apply_epoch() in process() just after creation.
But at this moment buffers are empty, so in example project in NetworkedController in method _apply_epoch I added checks for buffer size. Without checks it tries to read Vectors from empty buffers. And it will continue until server send real epoch.
But if you can add check for buffer size, you still get error because DollController calls seek() on empty buffer.

Attached example project for 3.x, ported for 4.0
Tested on Godot 4 alpha15 + NetSync
example-project-3.x.zip