perf hists browser: Reset selection when refresh

With the following steps:

 Step 1: perf report

 Step 2: Use UP/DOWN to select an entry, don't press 'ENTER'

 Step 3: Use '/' to filter symbols, use a filter which returns
         empty result

 Step 4: Press 'ENTER'

We see that, even if we have filtered all the symbols (and the main
interface is empty), pressing 'ENTER' still selects one symbol. This
behavior surprises the user.

This patch resets browser->{he_,}selection in hist_browser__refresh()
and lets it choose default selection. In this case
browser->{he_,}selection keeps NULL so user won't see annotation item in
menu.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1449455746-41952-4-git-send-email-wangnan0@huawei.com


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