VIC chip addressing fix

[aycock]

The VIC chip couldn't address the full 16-bit address space, and programmers took advantage of this to have access to both custom chars and in-ROM char sets at the same time. Here's one discussion of this: https://sleepingelephant.com/~sleeping/ipw-web/bulletin/bb/viewtopic.php?p=111327&sid=f729b55c1b19ce39fe779605640d517b#p111327

You can see the emulation bug if you run, say, Jeff Minter's Gridrunner (http://www.minotaurproject.co.uk/downloads/softography/vic20/gridrunner-vic20.zip) because the numbers won't display correctly.

If this line:

chips/systems/vic20.h

Line 567 in bd1ecff

uint16_t data = (sys->color_ram[addr & 0x03FF]<<8) | mem_rd(&sys->mem_vic, addr);

is changed to:
uint16_t data = (sys->color_ram[addr & 0x03FF]<<8) | mem_rd(&sys->mem_vic, addr & 0x3fff);
then it seems to fix the problem.