Fix escaped carriage return parsing

Found with go-fuzz

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>

json5_test.go

@@ -131,7 +131,8 @@ func TestJSON5Decode(t *testing.T) {
 	})
 }
 
-// found with go-fuzz
+// The tests below this comment were found with go-fuzz
+
 func TestQuotedQuote(t *testing.T) {
 	var v struct {
 		E string
@@ -143,3 +144,11 @@ func TestQuotedQuote(t *testing.T) {
 		t.Errorf(`expected "'", got %q`, v.E)
 	}
 }
+
+func TestInvalidNewline(t *testing.T) {
+	expected := "invalid character '\\n' in string literal"
+	var v interface{}
+	if err := Unmarshal([]byte("{a:'\\\r0\n'}"), &v); err == nil || err.Error() != expected {
+		t.Errorf("expected error %q, got %s", expected, err)
+	}
+}

scanner.go

@@ -500,8 +500,8 @@ func stateInStringEsc(resume func(s *scanner, c byte) int) func(s *scanner, c by
 // stateInStringEscCR is the state after reading `"\\r` during a quoted string.
 func stateInStringEscCR(resume func(s *scanner, c byte) int) func(s *scanner, c byte) int {
 	return func(s *scanner, c byte) int {
+		s.step = resume
 		if c == '\n' {
-			s.step = resume
 			return scanContinue
 		}
 		return resume(s, c)