Fix copy of line with len = 0

Fix copy of line with len = 0

When a line has no any character linelen is 0, so last = &term.line[y][MIN(lastx, linelen-1)]
generated a pointer to the end of the previous line. The best thing we can do in this case
is to add a newline, because we don't have a glyph to print (and consult its state of
wrapping).