code cleanup for file quicksearch backspace

[Roland Illig]

Egmont Koblinger wrote:
> Hi,
> 
> When in file quicksearch mode (^S or Alt-S) and the search string is empty,
> and I press backspace, then the ascii code of the backspace is put into the
> search buffer, just as if I pressed a regular letter, and then (since no
> filenames begin with backspace, at least on my system :-)) this will be
> removed some lines later in the code.

Committed. Thanks for reporting.

Roland