[Fizz] Ignore error if content node is gone#33068

We normally expect the segment to exist whatever the client does while streaming. However, when hydration errors at the root of the shell for a whole document render, then we clear nodes from body which can include our segments. We don't need them anymore because we switched to client rendering. It triggers an error accessing parent node which can safely be ignored. This just helps avoid confusion in this scenario. This also covers up the error in #33067. Which doesn't actually cause any visible problems other than error logging. However, ideally we wouldn't emit completeBoundary instructions if the boundary is inside a cancelled fallback.