tui: Fix newterm call for older ncurses

tui: Fix newterm call for older ncurses

Older versions of ncurses' newterm can't take NULL for their ofp and ifp
parameters. Newer versions can, and they fall back on stdout/stdin if
that is the case.

This patch explicitly passes stdout/stdin to the call to newterm to
avoid segfaulting with older ncurses.

gdb/Changelog:

2014-11-04  Simon Marchi  <simon.marchi@ericsson.com>

	* tui/tui.c (tui_enable): Pass stdout and stdin to newterm.