LCDGeneric switches to BANK(wLYOverrides)

Used to assume we were already in that bank, but since interrupts can occur during VBlank (and VBlank can change wram banks), it won't do so any more. Worst-case the write to rSCX will take 49 cycles, well below the 76 cycles in doublespeed in the worst-case timing window from STAT interrupt to mode 3.

home/lcd.asm

@@ -1,5 +1,6 @@
 LCDGeneric::
-; At this point it's assumed we're in WRAM bank 5!
+; Unlike vanilla, it's *not* assume we're in BANK(wLYOverrides),
+; since interrupts can now occur during VBlank
 	ldh a, [rLY]
 	cp SCREEN_HEIGHT_PX
 	jr c, .continue
@@ -8,12 +9,18 @@ LCDGeneric::
 	push bc
 	ld c, a
 	ld b, HIGH(wLYOverrides)
+	ldh a, [rSVBK]
+	push af
+	ld a, BANK(wLYOverrides)
+	ldh [rSVBK], a
 	ld a, [bc]
 	ld b, a
 	ldh a, [hLCDCPointer]
 	ld c, a
 	ld a, b
 	ldh [c], a
+	pop af
+	ldh [rSVBK], a
 	pop bc
 	pop af
 	reti