Don't offer to save credit cards with an empty or 0 month.

components/autofill/core/browser/validation.cc

Index: components/autofill/core/browser/validation.cc
diff --git a/components/autofill/core/browser/validation.cc b/components/autofill/core/browser/validation.cc
index debe05340d4283bfa62f191bc8733066e249e091..22a3c91fca1b0ef16eeb2e847a57b9e1182948ea 100644
--- a/components/autofill/core/browser/validation.cc
+++ b/components/autofill/core/browser/validation.cc
@@ -40,6 +40,9 @@ bool IsValidCreditCardExpirationDate(const base::string16& year,
 bool IsValidCreditCardExpirationDate(int year,
                                      int month,
                                      const base::Time& now) {
+  if (month < 1 || month > 12)
+    return false;
+
   base::Time::Exploded now_exploded;
   now.LocalExplode(&now_exploded);