diff --stat: do not count "unmerged" entries

Even though we show a separate *UNMERGED* entry in the patch and
diffstat output (or in the --raw format, for that matter) in
addition to and separately from the diff against the specified stage
(defaulting to #2) for unmerged paths, they should not be counted in
the total number of files affected---that would lead to counting the
same path twice.

The separation done by the previous step makes this fix simple and
straightforward.  Among the filepairs in diff_queue, paths that
weren't modified, and the extra "unmerged" entries do not count as
total number of files.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

diff.c

@@ -1669,12 +1669,14 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options)
 		struct diffstat_file *file = data->files[i];
 		uintmax_t added = file->added;
 		uintmax_t deleted = file->deleted;
-		if (!file->is_interesting && (added + deleted == 0)) {
+
+		if (file->is_unmerged ||
+		    (!file->is_interesting && (added + deleted == 0))) {
 			total_files--;
 			continue;
 		}
 
-		if (!file->is_binary && !file->is_unmerged) {
+		if (!file->is_binary) {
 			adds += added;
 			dels += deleted;
 		}

t/t4049-diff-stat-count.sh

@@ -44,7 +44,7 @@ test_expect_success 'binary changes do not count in lines' '
 	test_i18ncmp expect actual
 '
 
-test_expect_failure 'exclude unmerged entries from total file count' '
+test_expect_success 'exclude unmerged entries from total file count' '
 	git reset --hard &&
 	echo a >a &&
 	echo b >b &&