The last two commits fix issues with invalid key inputs:

• Adjust size on mem_copy to only copy the valid keyboard state from the SDL array, mem_zero the remaining mouse and joystick state at the beginning.
• Make sure keys and scancodes are within array bounds to prevent out of bound writes. Add missing scancode assignment to mouse wheel events and ignore scrolling in x direction.

This should at least prevent random segmentation faults when using currently unsupported keyboard layouts...