river-raid: Routine at 936F

936F: Handle old position attributes when sprite is at screen top (row 0).

When Y AND $F8 = 0, the sprite is in attribute row 0 (pixel rows 0-7). Instead of writing attributes to row 0, this routine wraps around and writes to the bottom of the viewport. This preserves row 0 as black, creating an 8-pixel blank zone where sprites are invisible. Adds $03DF (31 rows × 32 bytes - 1 = 991) to wrap the address, then subtracts $03DF after each row to maintain the wrap.
set_attr_wrap_old	936F	LD BC,$03DF	Add $03DF to HL to correct wrapped address. Restore and re-save BC.
	9372	ADD HL,BC
	9373	POP BC
	9374	PUSH BC
set_attr_wrap_old_loop	9375	LD (HL),A	Inner loop: write attribute A to HL, increment HL, decrement C, repeat for row width.
	9376	INC HL
	9377	DEC C
	9378	JR NZ,set_attr_wrap_old_loop
	937A	POP BC	After row: restore BC, add stride DE, decrement B, re-save BC. Subtract $03DF from HL to maintain wrap. Jump back to set_attr_old_outer_loop for next row.
	937B	ADD HL,DE
	937C	DEC B
	937D	PUSH BC
	937E	LD BC,$03DF
	9381	OR A
	9382	SBC HL,BC
	9384	POP BC
	9385	JP set_attr_old_outer_loop