gpgconf: Always use xmalloc.

* tools/gpgconf-comp.c: Fix spelling of "cannot".  Use log_assert
instead of a plain assert.
(gc_percent_escape, percent_deescape): Fail on malloc error.

It does not make sense to use xtryalloc and failing then anyway. We
also should use our wrappers and not a plain realloc. Everywhere
elese we use the non-formal "can't" so it is better to do the same
here.

• Signed-off-by: Werner Koch <wk@gnupg.org>