SeqNumUnwrapper::Unwrap now returns int64_t instead of uint64_t.

Bug: webrtc:10263
Change-Id: Idaeae6be01bd4eba0691226c958d70e114161ffd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127295
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Johannes Kron <kron@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27129}
diff --git a/modules/video_coding/frame_buffer2.cc b/modules/video_coding/frame_buffer2.cc
index e4def86..d382b2e 100644
--- a/modules/video_coding/frame_buffer2.cc
+++ b/modules/video_coding/frame_buffer2.cc
@@ -328,11 +328,8 @@
 }
 
 bool FrameBuffer::ValidReferences(const EncodedFrame& frame) const {
-  if (frame.id.picture_id < 0)
-    return false;
-
   for (size_t i = 0; i < frame.num_references; ++i) {
-    if (frame.references[i] < 0 || frame.references[i] >= frame.id.picture_id)
+    if (frame.references[i] >= frame.id.picture_id)
       return false;
 
     for (size_t j = i + 1; j < frame.num_references; ++j) {