As it removed the sample accounting for code when no symbol sort key is
given for 'perf report' TUI, it might not have allocated the
'struct annotated_source' yet.  Let's check if it's NULL first.

Fixes: 6cdd977e ("perf report: Do not collect sample histogram unnecessarily")
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240424230015.1054013-1-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>