use const key for new&unsaved locations

if the location does not have an id yet (was not stored in epi yet)
we will use a temporary key to avoid react warning

src/ui/reviewLocationsCollection.tsx

@@ -31,7 +31,7 @@ export default class ReviewLocationsCollection extends React.Component<ReviewLoc
       <div>
         {filter.showPoints &&
          locations.map(location =>
-          <ReviewLocationComponent key={location.id} location={location} showDialog={(e) => this.onLocationClick(e, location)} />
+          <ReviewLocationComponent key={location.id || "unsaved"} location={location} showDialog={(e) => this.onLocationClick(e, location)} />
         )}
       </div>)
   };