[syslinux] Isolinux command line text affected

[Sebastian Herbszt]

Михаил wrote:
> Hi. This issue was introduced in isolinux version 3.62.
>
> Best regards, Mike.

This issue is not limited to isolinux and should affect all derivatives.
It only manifests if one of the message files, in your case boot.msg, contains
a graphic. Since commit b2e6d915489d7af1177c75b961438be7cec140f0
("Switch the display file and graphics routines to using the getc stack)" the
command_line buffer is reused for VGARowBuffer in graphics.inc:

; We need a buffer of 640+80 bytes.  At this point, command_line should
; not be in use, so use that buffer.
VGARowBuffer   equ command_line

The content of command_line gets overwritten and you get garbage displayed
on the boot prompt.

- Sebastian