Fix copy/paste error when mapping the new buttons for P2.

[msheehan79]

Move R3 to its proper index for P2.

[BlazeEntertainment]

This is now OOB and will Seg fault if you load the core.

Update the sizes to something like:

int joypad0[20]; // joypad 0 state
int joypad1[20]; // joypad 1 state
int joypre0[20]; // joypad 0 previous state
int joypre1[20]; // joypad 1 previous state

To resolve the OOB and then it should fix the problem

[msheehan79]

Thanks @BlazeEntertainment for the catch. Will update this PR this evening to include this.

[cmitu]

@twinaphex any chance of merging this PR ? It would fix the core segfault/crash and make the core usable again.
Thank you.