Reject stale BUNDLE MIDs missing from descriptions

BundleManager keeps established BUNDLE groups across offers when the new offer does not include BUNDLE groups. ValidateAndMaybeUpdateBundleGroups() can therefore see stale MIDs that are absent from the current description.

Return INVALID_PARAMETER before dereferencing a missing content section while validating rejected BUNDLE groups.

Bug: webrtc:514442582
Change-Id: Ie592b03de7b92d20da6dc08969d7c2f7b79678e0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/473740
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Boris Tsirkin <btsirkin@meta.com>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47747}