Volex TTX2000 S Issue 1.2: Routine at 09B6

09B6: double_code: Handle double height control code.

Used by the routine at decode_row.
double_code	09B6	LD A,$01	Set double_height_flag.
	09B8	LD (double_height_flag),A	Set double_height_flag.
	09BB	LD (row_has_double_flag),A	Set row_has_double_flag.
	09BE	LD (skip_next_row_flag),A	Set skip_next_row_flag.
	09C1	LD A,$20	Set hold_mosaic_character to $20 (space character) and jump to code_set_at.
	09C3	LD (hold_mosaic_character),A
	09C6	JP code_set_at