fix(arnitech): INS in insert mode opens another space

In the spaces INS opened the Terminal driver sent INS to Literal, which
drew it as a glyph. On a C64 the INST key "inserts spaces normally" in
insert mode and shows as a reverse character only in quote mode
(Programmer's Reference Guide, the screen editor, p. 96), so INS now
goes to Output there and counts INSRT up when it opened a space.

src/kernal/arnitech/arnitech_terminal.s

@@ -29,8 +29,9 @@ terminal_find:
 ;
 ; Outside quote and insert mode the byte goes to Output. While either is on, every control code
 ; but RETURN, SHIFT+RETURN, and STOP goes to Literal, which draws it as a glyph; so does DEL
-; while INSRT is not 0, which a DEL between quotes leaves to delete. RETURN, SHIFT+RETURN, and
-; STOP end both modes. A glyph drawn counts INSRT down, a quote toggles QTSW, and an INS that
+; while INSRT is not 0, which a DEL between quotes leaves to delete, but INS then opens another
+; space, as on a C64 (Programmer's Reference Guide, p. 96). RETURN, SHIFT+RETURN, and STOP end
+; both modes. A glyph drawn counts INSRT down, a quote toggles QTSW, and an INS that
 ; opened a space (status bit 3) counts INSRT up.
 ;
 
@@ -78,7 +79,11 @@ chrout_terminal_control:
 	beq chrout_terminal_end_modes
 
 	ldy INSRT
-	bne chrout_terminal_literal        ; in the spaces INS opened, DEL too is a glyph
+	beq @1
+	cmp #KEY_INS
+	beq chrout_terminal_code           ; in the spaces INS opened, INS opens another
+	bne chrout_terminal_literal        ; ... and DEL too is a glyph
+@1:
 	ldy QTSW
 	beq chrout_terminal_code
 	cmp #KEY_DEL