More low colour mode alignment drawing problems

[rakslice]

In 16 colours or less modes with screen width not giving a row size aligned with bytes, i.e.

• Black and white mode and screen width not a multiple of 8 pixels,
• 4 grays/colours modes and screen width not a multiple of 4 pixels, or
• 16 grays/colours modes and screen width not a multiple of 2 pixels

gives a screen truncated on the right, with draws wrapping around

• BII & SS
• VOSF and non-VOSF