When Writer creates an embedded data source definition, it should be
stored on the storage of the Writer document, so Writer sets the
TargetStorage and StreamRelPath parameters of the storeAsURL() call.

Let ODatabaseDocument::impl_storeAs_throw() and
ODatabaseDocument::impl_writeStorage_throw() respect these, so the save
actually succeeds.

Change-Id: I4568ef96204a219b813142d7b5eebe9f1ec5e22e