Check InternalList node exists when rendering MWReferenceList

If you've just pasted in a reference and a list the internal list
nodes may not have been rebuilt yet.

Bug: 58242
Change-Id: Ib10b81f4023194791f789f3e7dda393f2e355ea3
(cherry picked from commit 5f78aa22f11267c84f9dcca78f36732a7c0b01ea)