ciolib_movetext: Plug fill buffer memory leak

This fixes a memory leak in ciolib_movetext() which accumulates
memory very quickly in scroll heavy ncurses environments. The
problem was originally noticed while running syncterm, and
confirmed with valgrind.

valgrind confirmation:

 17,310,720 bytes in 368 blocks are definitely lost in loss record 128 of 128
    at 0x8C82899: malloc
    by 0x16E273: ciolib_movetext (ciolib.c:563)
    <<snip>>