Before we had an assert that would catch if a sample had an
invalid times, however input may have bad times.
We did have a message if we saw a sample with a duration equal to
zero. This expands that check to check if the time is valid in
general and will ignore any sample that is not valid.
Fixes#425
Change-Id: I9774bfbdbd401f3016d2c345665b9973d1889db7