API: improve validation message greater/lower than

Add translation and return a better error for lower than

internal/routes/userbookputupdate.go

@@ -68,6 +68,7 @@ func PutUserBookHandler(ac appcontext.AppContext) {
 		err = validateRating(*userBookPut.Rating)
 		if err != nil {
 			myvalidator.ReturnErrorsAsJsonResponse(&ac, err)
+			return
 		}
 		updateRating(&userbook, &userBookPut)
 	}