Mark connection as closed on send error.

I would have expected that no matter what causes the TCP connection to be closed would be reported as a TCP call back with lenghth = -1. However there are scenarios where this isn't true. I.e. when the user aborts during a blocking TCP retransmit opration. I'm unsure if this behaviour is to be considered a bug or if this is by some design I don't understand.

So I opted to not change that behaviour but rather add an explicit check for tcp_send returning with an error indicating that the connection is closed. This way the users gets noticed on the closed connection at least on his next key press.

apps/telnet65.s

@@ -306,6 +306,12 @@ send_char:
   jsr tcp_send
   bcs :+
   rts
+: lda ip65_error
+  cmp #KPR_ERROR_CONNECTION_CLOSED
+  bne :+
+  lda #1
+  sta connection_closed
+  rts
 : ldax #send_error
   jsr print_ascii_as_native
   jmp print_error