ScanningResultIterator should not time out a query after receiving a valid result

Phoenix query time includes setting up scanners and retrieving the very first result from each of these scanners. The query timeout check in ScanningResutIterator introduced by PHOENIX-6918 extends the query timeout check beyond the first result from a given scanner. ScanningResutIterator should not check if query timeout after the first valid (not dummy) result from the server.