BibIndex: virtual index queue dupe optimisation

• Before indexing virtual index, let us remove duplicate entries in queue table. It will save indexing time, because the same actions won't have to be performed twice.

Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>