t4012: Use test_must_fail instead of if-else

Make the code less bulky and easier to read. Also do not overlook
failures like e.g. git failing because of unexpected signals.

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

t/t4012-diff-binary.sh

@@ -66,13 +66,7 @@ test_expect_success 'apply --numstat understands diff --binary format' '
 test_expect_success 'apply detecting corrupt patch correctly' '
 	git diff >output &&
 	sed -e "s/-CIT/xCIT/" <output >broken &&
-	if git apply --stat --summary broken 2>detected
-	then
-		echo unhappy - should have detected an error
-		(exit 1)
-	else
-		echo happy
-	fi &&
+	test_must_fail git apply --stat --summary broken 2>detected &&
 	detected=`cat detected` &&
 	detected=`expr "$detected" : "fatal.*at line \\([0-9]*\\)\$"` &&
 	detected=`sed -ne "${detected}p" broken` &&
@@ -81,13 +75,7 @@ test_expect_success 'apply detecting corrupt patch correctly' '
 
 test_expect_success 'apply detecting corrupt patch correctly' '
 	git diff --binary | sed -e "s/-CIT/xCIT/" >broken &&
-	if git apply --stat --summary broken 2>detected
-	then
-		echo unhappy - should have detected an error
-		(exit 1)
-	else
-		echo happy
-	fi &&
+	test_must_fail git apply --stat --summary broken 2>detected &&
 	detected=`cat detected` &&
 	detected=`expr "$detected" : "fatal.*at line \\([0-9]*\\)\$"` &&
 	detected=`sed -ne "${detected}p" broken` &&