A malformed PDF can store a non-dictionary object under a page's /Font or
/XObject resource. find_nonembedded_cid_fonts() iterated .values() on that
object outside the per-entry try/except, so scanning such a page raised
(TypeError/AttributeError depending on the pikepdf version) instead of
producing output. This surfaced as a PDF/A conversion crash.
Route both resource lookups through a small helper that returns an empty
list when the resource is missing or not a dictionary, so a garbage entry
is simply treated as having no fonts. Add a regression test covering a
non-dictionary /Font and /XObject.
