BibDocFile: register downloads with recid

* Adds self.recid when calling `register_download()`.
  (closes #1831) (closes #1832)

Signed-off-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
WebSearch: fix for 'rhs is of unknown type'

* Fixes TypeError in search_engine that was occurring when a new
  collection has been added but the webcoll has not yet been run.
  (closes #1819)

Signed-off-by: Sebastian Witowski <sebastian.witowski@cern.ch>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>