perf ui browser: Avoid SEGV on title

If the title is NULL then it can lead to a SEGV.

Fixes: 769e6a1e15bdbbaf ("perf ui browser: Don't save pointer to stack memory")
Signed-off-by: Ian Rogers <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Leo Yan <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/ui/browser.c

···
 void ui_browser__handle_resize(struct ui_browser *browser)
 {
 	ui__refresh_dimensions(false);
-	ui_browser__show(browser, browser->title, ui_helpline__current);
+	ui_browser__show(browser, browser->title ?: "", ui_helpline__current);
 	ui_browser__refresh(browser);
 }