Fix of document embedding
Fix of document embedding

KeyError exception was raised when field specified in schema as embeddable
was missing in a particular document.

mcreenan/eve,superdesk/eve,EasonYi/eve,jzorrof/eve,amagdas/eve,hustlzp/eve,opticode/eve,mugurrus/eve,kalbasit/eve,kidaa/eve,eduardomb/eve,matthieuprat/eve,pjs7678/eve,julianhille/eve,sebest/eve,elpoisterio/eve,bcrochet/eve,yanyanqin/eve,stratosgear/eve