perf tui: Reset use_browser if stdout is not a tty

The newt initialization routines weren't being called because the output
was a file (perf annotate > /tmp/bla) but use_browser was still 1,
because ~/.perfconfig had it as 'on', so, later on newt routines
segfaulted.

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>