The memory for this format is now statically allocated as well. I
was under the impression its size would depend on wincols, but this is
the format we're talking about, the string does not have to hold the
actual line contents. I must have been sleeping again...

Oh well, this is a slight performance improvement, although it doesn't
seem the be the cause of the browing slowness when running under
valgrind. (Obviously running ncdu with valgrind is supposed to be
slower, but the current performance is rather bad...)