col: make flush_line() a little bit robust

col: make flush_line() a little bit robust

The code is horrible. The core of the problem are signed integers
and no check for the limits.

This patch fixes c->c_column = cur_col; where c_column is "short"
and "cur_col" is int. Let's use "int" for all the variables. It's
really not perfect as for bigger lines it can segfault again...

The patch also removes some unnecessary static variables.

Addresses: https://github.com/karelzak/util-linux/issues/749
Signed-off-by: Karel Zak <kzak@redhat.com>