fix: tiles off command causes system lockup (#93)

The tiles off path skipped the ply that balances the phy at entry
to TileSwitch, corrupting the return address on the hardware stack.

Author: mbrukner

source/system.f256/module.interfaces/graphics/gcontrol.asm

@@ -188,7 +188,7 @@ TileSwitch:
 		lda 	#GCMD_TileCtl
 		jsr 	GXGraphicDraw
 		plx
-		bpl 	TilesCtrlLoop 				; nothing else.
+		bpl 	_TileSwitchDone 			; OFF: skip size/scroll setup
 
 		lda 	#GCMD_TileSize 				; set size of tile map.
 		ldx 	TileMapWidth
@@ -199,6 +199,7 @@ TileSwitch:
 		jsr 	_TileResetScroll
 		lda 	#GCMD_TileScrollY
 		jsr 	_TileResetScroll
+_TileSwitchDone:
 		ply
 		bra 	TilesCtrlLoop