A packet's capture time may be -1 to indicate an unset value. We need to check that this is the case before adjusting it when generating padding. Otherwise, invalid values will result. Bug: webrtc:11615 Change-Id: Ibbeb959f1d4d37dd4d65702494b97246642b57d6 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176281 Commit-Queue: Dan Minor <dminor@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Cr-Commit-Position: refs/heads/master@{#31766}