column: fix greedy mode on -l

column: fix greedy mode on -l

In the 'greedy' mode strtok() skips leading white chars, but code for
-l (merge remaining data to the last column) do not count the skipped
chars.

Old version:

$ printf '  a b c\n1 2 3\n' | column -t -o '-' -l2
a-a
1-2 3

Fixed version:

$ printf '  a b c\n1 2 3\n' | column -t -o '-' -l2
a-b c
1-2 3

Note, see leading white chars '  a b c'.

Fexes: https://github.com/util-linux/util-linux/issues/1763
Signed-off-by: Karel Zak <kzak@redhat.com>