The SpatialIndex value from an EncodedImage is 0-based, but values were
off by 1.
Bug: none
Change-Id: Ie74e6450ddef1cfaee68fa230c441030fa86a64a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/203525
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33067}