GLWidgets::reloadEngines() - no proof from corrupted or incompatible settins

I’ve spend a lot of time trying to figure out why half ow engines disappeared from “Display Types” (however being visible in Settings dialog). Problem was resolved after removing of settings file. I think there must be some sort of “protection” from missing engines. It’s ok to store list in settings to keep duplicated engines, but check is needed if all loaded engines are present at least one time