diff: Only count lines in show_shortstats

Do not mix byte and line counts. Binary files have byte counts;
skip them when accumulating line insertions/deletions.

The regression was introduced in e18872b.

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -1668,7 +1668,7 @@ static void show_shortstats(struct diffstat_t *data, struct diff_options *option
 			continue;
 		if (!data->files[i]->is_renamed && (added + deleted == 0)) {
 			total_files--;
-		} else {
+		} else if (!data->files[i]->is_binary) { /* don't count bytes */
 			adds += added;
 			dels += deleted;
 		}

t/t4012-diff-binary.sh

@@ -36,6 +36,18 @@ test_expect_success '"apply --stat" output for binary file change' '
 	test_i18ncmp expected current
 '
 
+test_expect_success 'diff --shortstat output for binary file change' '
+	echo " 4 files changed, 2 insertions(+), 2 deletions(-)" >expected &&
+	git diff --shortstat >current &&
+	test_i18ncmp expected current
+'
+
+test_expect_success 'diff --shortstat output for binary file change only' '
+	echo " 1 file changed, 0 insertions(+), 0 deletions(-)" >expected &&
+	git diff --shortstat -- b >current &&
+	test_i18ncmp expected current
+'
+
 test_expect_success 'apply --numstat notices binary file change' '
 	git diff >diff &&
 	git apply --numstat <diff >current &&