Making it clear that safe_strtou64 kind of string to int conversion apis fail when non decimal chars are present. (#2744)

cpp/src/phonenumbers/stringutil.cc

@@ -293,4 +293,4 @@ void StrAppend(string* dest, const StringHolder& s1, const StringHolder& s2,
 }
 
 }  // namespace phonenumbers
-}  // namespace i18n
+}  // namespace i18n

cpp/test/phonenumbers/stringutil_test.cc

@@ -135,7 +135,7 @@ TEST(StringUtilTest, safe_strtou64) {
   safe_strtou64("16", &n);
   EXPECT_EQ(16U, n);
 
-  safe_strtou64("18446744073709551615UL", &n);
+  safe_strtou64("18446744073709551615", &n);
   EXPECT_EQ(18446744073709551615ULL, n);
 }