download-from-binary-cache.pl: Fix race condition
download-from-binary-cache.pl: Fix race condition

Fixes the error "DBD::SQLite::db do failed: column url is not unique".

NixOS/nix,tchajed/nix,acowley/nix,edolstra/nix,zimbatm/nix,dtzWill/nix,NixOS/nix,gridaphobe/nix,bjornfor/nix,jcumming/nix,rycee/nix,bennofs/nix,ysangkok/nix,zimbatm/nix,garbas/nix,shlevy/nix,joelmo/nix,pikajude/nix,joelmo/nix,vizanto/nix,joelmo/nix,nbp/nix,bennofs/nix,tchajed/nix,bjornfor/nix,puffnfresh/nix,garbas/nix,shlevy/nix,rowhit/nix,ehmry/nix,garbas/nix,vcunat/nix,ysangkok/nix,acowley/nix,layus/nix,dezgeg/nix,dtzWill/nix,aucampia/nix,peti/nix,shlevy/nix,layus/nix,offlinehacker/nix,rowhit/nix,dezgeg/nix,nbp/nix,ttuegel/nix,ehmry/nix,acowley/nix,nbp/nix,pikajude/nix,dtzWill/nix,ttuegel/nix,shlevy/nix,rowhit/nix,peti/nix,ehmry/nix,bjornfor/nix,tchajed/nix,puffnfresh/nix,wmertens/nix,garbas/nix,layus/nix,bjornfor/nix,zimbatm/nix,edolstra/nix,puffnfresh/nix,ysangkok/nix,layus/nix,rycee/nix,gebner/nix,dtzWill/nix,aucampia/nix,shlevy/nix,offlinehacker/nix,vcunat/nix,ehmry/nix,vizanto/nix,aucampia/nix,gridaphobe/nix,peti/nix,ehmry/nix,bennofs/nix,NixOS/nix,vizanto/nix,rycee/nix,ttuegel/nix,gebner/nix,tchajed/nix,vizanto/nix,zimbatm/nix,wmertens/nix,dtzWill/nix,offlinehacker/nix,jcumming/nix,gebner/nix,wmertens/nix,offlinehacker/nix,gridaphobe/nix,layus/nix,edolstra/nix,NixOS/nix,garbas/nix,gebner/nix,NixOS/nix,jcumming/nix,jcumming/nix,puffnfresh/nix,gridaphobe/nix,rowhit/nix,edolstra/nix,vcunat/nix,peti/nix,aucampia/nix,joelmo/nix,nbp/nix,ttuegel/nix,acowley/nix,dezgeg/nix,peti/nix,wmertens/nix,dezgeg/nix,edolstra/nix,vcunat/nix,rycee/nix,pikajude/nix,ehmry/nix,rycee/nix,dezgeg/nix,bennofs/nix