WebSubmit: Link_Records error message fix

* Fixes the bug in str.join(recids) in get_recid_and_reportnumber function;
  recids should be converted to strings before calling join function.
  (PR #1734)

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