There is no obvious case where such a fallback would be needed, but it
does introduce a bug with a delete redline inside a hidden section:
on Show, when moving the nodes into the body content,
FindPrvNxtFrameNode() will return nullptr because there are no frames
inside the hidden section, but then this fallback will cause it to
erroneously create a frame.

Change-Id: I2328a6f213fdec95857b6e4446e1a8504c17f599