perf hists browser: Allow thread filtering for comm sort key

The commit 2eafd410

 ("perf hists browser: Only 'Zoom into thread'
only when sort order has 'pid'") disabled thread filtering in hist
browser for the default sort key.  However the he->thread is still valid
even if 'pid' sort key is not given.  Only thing it should not use is
the pid (or tid) of the thread.  So allow to filter by thread when
'comm' sort key is given and show pid only if 'pid' sort key is given.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1457536490-24084-1-git-send-email-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>