perf tools: Fix report -F abort for data without branch info

The branch field sorting code assumes hist_entry::branch_info is
allocated, which is wrong and following perf session ends up with report
segfault.

  $ perf record ls
  $ perf report -F abort
  perf: Segmentation fault

Checking that hist_entry::branch_info is valid and display "N/A" string
in snprint callback if it's not.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1413468427-31049-2-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/sort.c

@@ -989,6 +989,9 @@ struct sort_entry sort_mem_dcacheline = {
 static int64_t
 sort__abort_cmp(struct hist_entry *left, struct hist_entry *right)
 {
+	if (!left->branch_info || !right->branch_info)
+		return cmp_null(left->branch_info, right->branch_info);
+
 	return left->branch_info->flags.abort !=
 		right->branch_info->flags.abort;
 }
@@ -996,10 +999,15 @@ sort__abort_cmp(struct hist_entry *left, struct hist_entry *right)
 static int hist_entry__abort_snprintf(struct hist_entry *he, char *bf,
 				    size_t size, unsigned int width)
 {
-	static const char *out = ".";
+	static const char *out = "N/A";
 
+	if (he->branch_info) {
 		if (he->branch_info->flags.abort)
 			out = "A";
+		else
+			out = ".";
+	}
+
 	return repsep_snprintf(bf, size, "%-*s", width, out);
 }