net/http: add corner cases for readCookiesTests

The following corner cases for readCookiesTests are tested now:
 - An extra cookie delimiter ";" at the end of a Cookie header
 - An empty Cookie header

Change-Id: Id8028b448e4182613fb261bf0903efc98cbf4997
Reviewed-on: https://go-review.googlesource.com/c/go/+/164702
Reviewed-by: Volker Dobler <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>
Run-TryBot: Emmanuel Odeke <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: Asuan

src/net/http/cookie_test.go

@@ -385,6 +385,19 @@ var readCookiesTests = []struct {
 			{Name: "c2", Value: "v2"},
 		},
 	},
+	{
+		Header{"Cookie": {`Cookie-1="v$1"; c2=v2;`}},
+		"",
+		[]*Cookie{
+			{Name: "Cookie-1", Value: "v$1"},
+			{Name: "c2", Value: "v2"},
+		},
+	},
+	{
+		Header{"Cookie": {``}},
+		"",
+		[]*Cookie{},
+	},
 }
 
 func TestReadCookies(t *testing.T) {