[syslinux] ISOLINUX 5.00 TEXT HELP directive hang

[Ady]

Conditions to trigger this bug(s):

1_ Boot with ISOLINUX (SYSLINUX seems fine).
2_ Do NOT use the UI directive.
3_ In between TEXT HELP - ENDTEXT directives, use more than one line 
of text.

   *** syslinux.cfg start ***
DEFAULT vesamenu.c32
PROMPT 0

LABEL pwd1
COM32 pwd.c32
TEXT HELP
one line of text
two lines of text
ENDTEXT
   *** syslinux.cfg end ***

Result: the system ([vesa]menu) hangs.

So for whichever reason, the text (specifically, LF/CR or related 
characters) in between TEXT HELP - ENDTEXT directives is being 
"parsed", instead of being "just displayed". This hangs [vesa]menu.


Observations:
1_ In a VM with the above conditions, menu.c32 hangs, and 
vesamenu.c32 completely crashes the VM.
2_ If the cli prompt is shown (with PROMPT 1 for example) before 
[vesa]menu, the system boots. When an attempt to start [vesa]menu is 
made (press enter to activate the default entry in the example 
above), the system hangs.
3_ If the text in between TEXT HELP - ENDTEXT directives has only one 
line, the system does not hang.
4_ Using the UI directive avoids the hang too, independently of the 
amount of lines in between  TEXT HELP - ENDTEXT directives.

Please fix this problem for the next (pre)release, so current cfg 
files can still be used with ISOLINUX 5.xx.

TIA,
Ady.