Avoid sign extension when comparing mtime with Instant#getEpochSecond

Avoid sign extension when comparing mtime with Instant#getEpochSecond

Ensure we use the same type when comparing seconds since the epoch.

This does not prevent that in 2038 timestamps in seconds since the epoch
stored in a 32 bit integer will overflow. Integer.MAX_VALUE translates
to 2038-01-19T03:14:07Z. After this date we'll have an issue since we
store seconds since the epoch in a 32 bit integer in some places.

Bug: 319142
Change-Id: If0c03003d40b480f044686e2f7a2f62c9f4e2fe1
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>