perf hists browser: Show folded sign properly on --hierarchy

perf hists browser: Show folded sign properly on --hierarchy

When horizontal scrolling is used in hierarchy mode, the folded signed
disappears at the right most column.

Committer note:

To test it, run 'perf top --hierarchy, see the '+' symbol at the first
column, then press the right arrow key, the '+' symbol will disappear,
this patch fixes that.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20161108130833.9263-3-namhyung@kernel.org
[ Move 'width -= 2' invariant to right after the if/else ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>