perf annotate-data: Check if 'struct annotation_source' was allocated on 'perf report' TUI

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.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>