Indexing Vocabularies with bnode and LDPath does not work

STANBOL-765 added support for indexing bnodes by converting them to URIs. As it turns out when doing so the org.apache.stanbol.entityhub.indexing.core.processor.LdpathSourceProcessor can no longer follow paths with a bnode representing one of the traversed resources.

The reason for that is that the Bnode is converted to an URI but the RDFBackendImplementation of the Jena TDB indexing source does not convert the parsed URI based to a Bnode before looking it up in the triple store.