ciolib_movetext: Do not leak fill buffer

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) <>