perf tools: Fix column alignment when headers aren't shown on TUI

If user sets ui.show-headers config option to false, it didn't
calculate default column width so it broke the alignment.  This is
because it does the calculation just before showing headers.

Move it to the beginning of the hist browser so that it can be called
regardless of the config option.

Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>