Border colour drop down list on Vic 20 needs to be restricted to 8 colours

[AndyHOvine]

To avoid confusion, the Vic 20's Border colour dropdown needs to be restricted to colours 0-7 as these are the only valid values allowed.

Note: The C64 is not affected (it has Aux 1 and Aux 2) and the Vic 20's Aux colour is not affected. These are allowed the 16 colours.