Bug in Loro: Unreachable code when loroMap is in directely in LoroDocument

[kulla]

https://github.com/loro-dev/loro-prosemirror/blob/83621a713212deacb73c2c48c68660aa014af858/src/cursor/common.ts#L383-L411 assumes that the root prosemirror node has no parents which is not true when loro map is included in a bigger document