SearchEngineSummarizer: creating WarehouseSummarizer instances unnecessarily

We only need to create a WarehouseSummarizer in the
WarehouseSummarizerSearchEngineAccountDispatcher if the # of total rows of data
summarized by the SearchEngineAccountWorkers for a particular account > 0.

To fix this, we need to keep track of the # of rows in summarized, and in the
summarizeWarehouseData() method we can say

if (thePreventWHSummFlag) {
...
}
else if (getNumDataRowsForCurrentAccount() > 0) {
WarehouseSummarizer whsumm = new WarehouseSummarizer();
...
}
else {
// Skipping Account getAccountIDs();
}

Note: This might cause issues with Warehouse data availability being gray, so we
may need to do some additional work to set warehouse data availability for that
distribution, so data availability will still be set the same way it is now.