ScanResumer.resume would perform unnecessary scan when close AsyncTableResultScanner

When we invoke AsyncTableResultScanner.close, AsyncTableResultScanner.resultQueue is cleared and AsyncTableResultScanner.closed is set to true, and we do not need any more scan results. But if there is a ScanResumser, ScanResumer.resume would be invoked to perform another unnecessary scan on RegionServer and call AsyncTableResultScanner.onNext again when ScanResponse is received. AsyncTableResultScanner.onNext would do nothing else but just discard scan results because AsyncTableResultScanner.closed is true. We could save this unnecessary scan on RegionServer and close scanner directly .