@unnumbered sections, FastBack and FastForward

Hi,

$T2H_NAME{FastBack}, $T2H_HREF{FastBack},  $T2H_NODE{FastBack} are undefined
(and the same for FastForward,  Prev, Next) in case of a unnumbered section
associated with a node without reference to other node.

Example in texinfo manual:
@node Copying Conditions
@unnumbered Texinfo Copying Conditions

I detected it because I test with perl -w and thus undefined things appear.
It would be easy to add the proper tests to avoid the warnings. However I am 
not certain whether having *{FastForward} and *{FastBack} undef is right or 
wrong (*{Prev} and *{Next} are not used in the default setting, thus are of 
less interest). Having *{FastForward} and *{FastBack} undef, in the end
leads to the FastForward and FastBack buttons to be unclickable. Another
possibility would be to have FastForward and Forward buttons similars, and
FastBack and Back buttons similar. Any thoughts ?

Pat