reflect: Fix Kind(-1).String() and enable test

src/reflect/all_test.go

@@ -8021,6 +8021,8 @@ func TestIssue50208(t *testing.T) {
 	}
 }
 
+*/
+
 func TestNegativeKindString(t *testing.T) {
 	x := -1
 	s := Kind(x).String()
@@ -8030,8 +8032,6 @@ func TestNegativeKindString(t *testing.T) {
 	}
 }
 
-*/
-
 type (
 	namedBool  bool
 	namedBytes []byte

src/reflect/type.go

@@ -116,6 +116,8 @@ const Ptr = Pointer
 
 func (k Kind) String() string {
 	switch k {
+	case Invalid:
+		return "invalid"
 	case Bool:
 		return "bool"
 	case Int:
@@ -169,7 +171,7 @@ func (k Kind) String() string {
 	case Struct:
 		return "struct"
 	default:
-		return "invalid"
+		return "kind" + itoa.Itoa(int(int8(k)))
 	}
 }