Atari: fix stray cursor image when connecting to BSDs.

FreeBSD and NetBSD, at least, have a banner message when you telnet into them
which has an empty line as first line. On those systems, an old "cursor" char
was visible at the top of the login prompt message.
This is fixed by enabling and disabling the cursor in 'get_key' while waiting
for a key press.

drivers/atrinput.s

@@ -9,6 +9,7 @@
 .exportzp abort_key_disable = 0
 
 .import ip65_process
+.import print_a
 
 
 .data
@@ -75,8 +76,26 @@ special_key_table2:
 ; inputs: none
 ; outputs: A contains ASCII value of key just pressed
 get_key:
+  lda #0
+  sta CRSINH                    ; cursor on
+  ; according to "Mapping the Atari", a change to CRSINH will only be in effect after the next cursor movement,
+  ; so we move the cursor one to the left and then one to the right (to keep its original position)
+  lda #ATLRW
+  jsr print_a
+  lda #ATRRW
+  jsr print_a
+@loop:
   jsr get_key_if_available
-  bcc get_key
+  bcc @loop
+  ldy #1
+  sty CRSINH                    ; cursor on
+  tay                           ; save key
+  ; see above comment wrt. "Mapping the Atari"
+  lda #ATLRW
+  jsr print_a
+  lda #ATRRW
+  jsr print_a
+  tya                           ; restore key
   rts
 
 ; inputs: none