coverity#1257109 Unchecked dynamic_cast

and

coverity#1257108 Unchecked dynamic_cast

Change-Id: Ib0d42b7fcd3b2b87a95301b111cebe80f54dd13f
coverity#1257114 Result is not floating-point

Change-Id: I420fa77d52ca72a4c4609b4610572b8735911b4b
coverity#735379 annotate to dismiss Copy-paste error

on the basis that it doesn't look obviously wrong to the original author after
a once-over

Change-Id: If333a17a2a9954d33ebefc6846e40e0e1e29c857
writer won't allow us to enter multiple CrossRefBookmarks on the same node

e.g. fdo63164-1.docx and loads more like that, and the .docx genuinely has
multiple bookmarks at the same place, so just allow the first one and discard
the following ones

Change-Id: Ida2f5d79fdef4ed3e2d8c1e96ca6a086004f6c7d