perf hists browser: React to unassigned hotkey pressing

When that happens we were just ignoring the key press, now this
message is presented in the bottom line (the help line):

  "Press '?' for help on key bindings"

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-iyma2j5kj3q9i1stl4mfh90n@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/browsers/hists.c

@@ -1902,10 +1902,11 @@ static int perf_evsel__hists_browse(struct perf_evsel *evsel, int nr_events,
 		case CTRL('c'):
 			goto out_free_stack;
 		case 'f':
-			if (is_report_browser(hbt))
-				continue;
-			goto out_free_stack;
+			if (!is_report_browser(hbt))
+				goto out_free_stack;
+			/* Fall thru */
 		default:
+			helpline = "Press '?' for help on key bindings";
 			continue;
 		}