test: "am -3" can accept non-standard -p<num>

This adds a test for the previous one to make sure that "am -3 -p0" can
read patches created with the --no-prefix option.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t4150-am.sh

@@ -123,6 +123,7 @@ test_expect_success setup '
 	git commit -m "added another file" &&
 
 	git format-patch --stdout master >lorem-move.patch &&
+	git format-patch --no-prefix --stdout master >lorem-zero.patch &&
 
 	git checkout -b rename &&
 	git mv file renamed &&
@@ -276,6 +277,20 @@ test_expect_success 'am -3 falls back to 3-way merge' '
 	git diff --exit-code lorem
 '
 
+test_expect_success 'am -3 -p0 can read --no-prefix patch' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout -b lorem3 master2 &&
+	sed -n -e "3,\$p" msg >file &&
+	head -n 9 msg >>file &&
+	git add file &&
+	test_tick &&
+	git commit -m "copied stuff" &&
+	git am -3 -p0 lorem-zero.patch &&
+	! test -d .git/rebase-apply &&
+	git diff --exit-code lorem
+'
+
 test_expect_success 'am can rename a file' '
 	grep "^rename from" rename.patch &&
 	rm -fr .git/rebase-apply &&