perf report: Use the right symbol for annotation

In non symbolic views, i.e. --sort without "symbol", as in:

 perf report --sort comm

We're segfaulting in the --tui because we're testing the symbol resolved
and then trying to use the symbol on the histogram entry where we're
coalescing all hits for a COMM, and the first hist_entry for a comm may
have a NULL symbol, i.e. the RIP didn't resolve to any symbol.

In this case we're segfaulting, fix it by testing against the symbol in
the histogram entry.

Reported-by: William Cohen <wcohen@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
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-8ylwubbcmu27ucc9ffrku3yv@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>