function readGap(iGapStart0, iGapEnd) {
			aReadPromises.push(
				that.readGap(oGapParent, iGapStart0, iGapEnd, oGroupLock.getUnlockedCopy(),
					fnDataRequested));
		}
Returns a promise to be resolved with an OData object for a range of the requested data.

@param {number} iIndex
  The start index of the range
@param {number} iLength
  The length of the range; <code>Infinity</code> is supported
@param {number} iPrefetchLength
  The number of rows to read before and after the given range; with this it is possible to
  prefetch data for a paged access. <code>Infinity</code> is supported.
@param {sap.ui.model.odata.v4.lib._GroupLock} oGroupLock
  A lock for the group to associate the requests with
@param {function} [fnDataRequested]
  The function is called just before a back-end request is sent.
  If no back-end request is needed, the function is not called.
@returns {sap.ui.base.SyncPromise}
  A promise to be resolved with the requested range given as an OData response object (with
  "@odata.context" and the rows as an array in the property <code>value</code>, enhanced
  with a number property <code>$count</code> representing the element count on server-side;
  <code>$count</code> may be <code>undefined</code>, but not <code>Infinity</code>). If an
  HTTP request fails, the error from the _Requestor is returned.
  The promise is rejected if a conflicting {@link #collapse} happens before the response
  arrives, in this case the error has the property <code>canceled</code> with value
  <code>true</code>.
@throws {Error} If given index or length is less than 0, or if
  <code>iPrefetchLength !== 0</code> is used while reading a grand total row separately

@public
@see sap.ui.model.odata.v4.lib._CollectionCache#read