1 extra frame of input lag

[Tatsuya79]

There's 1 additional frame of input lag in this core vs Genesis+GX.

Tested on Sonic 1:
game on pause, jump button pushed down, K hotkey to go to next frame = jumps on 3rd frame.

[irixxxx]

It's probably due to how picodrive synchronizes the output. The rendered output is sent to the display at the end of vsync. However, normally the next frame is calculated during vsync, so the displayed frame is actually late.