perf hists browser: Refuse 'a' hotkey on non symbolic views

We don't allocate the histogram data structures for --sort lists without
"sym", so, just like was done for the menu, don't try to annotate when
'a' is pressed, just warn the user about it.

Reported-by: David Ahern <dsahern@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-27mjg02s2mbw8lfxqv7jpzec@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>