function addElementsLater(oCache, aReadElements, iOffset) {
		return SyncPromise.resolve(Promise.resolve()).then(function () {
			// so that oCache.aElements is actually filled
			addElements.call(oCache, aReadElements, iOffset);
		});
	}
Returns a promise which resolves just when the given elements have been copied into the given
aggregation cache.

@param {sap.ui.model.odata.v4.lib._AggregationCache} oCache
  The cache
@param {object|object[]} aReadElements
  The elements from a cache read, or just a single one
@param {number} iOffset
  The offset within aElements
@returns {sap.ui.base.SyncPromise}
  An async promise for timing

@private
@see addElements