Handle invalid expiration time in `TokenInfo`

[RickyLB]

Description:

This PR temporarily handles an integer overflow for tokens that do not have an expiry time. Fetching TokenInfo expiry.seconds from the mirror node results in a Some(Timestamp { seconds: -9223372036854775808, nanos: 0 }) if the token's expiration time is not set.

Related issue(s):

• https://github.com/hashgraph/hedera-sdk-rust/issues/784

Fixes #

Notes for reviewer:

Checklist

• [ ] Documented (Code comments, README, etc.)
• [ ] Tested (unit, integration, etc.)