HPCC-18424 Alien datatype failures

Temporarily disable new prefetch code until it can handle alien datatypes.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>

rtl/eclrtl/rtlrecord.cpp

@@ -554,7 +554,10 @@ ISourceRowPrefetcher * COutputMetaData::createDiskPrefetcher(ICodeContext * ctx,
     ISourceRowPrefetcher * fetcher = defaultCreateDiskPrefetcher(ctx, activityId);
     if (fetcher)
         return fetcher;
-    return new CDefaultPrefetcher(queryRecordAccessor(true));
+//  Should do something like this, if the flag existed...
+//  if (!getMetaFlags() & MDFhasaliendatatype_or_ifblock)
+//      return new CDefaultPrefetcher(queryRecordAccessor(true));
+    return new CSimpleSourceRowPrefetcher(*this, ctx, activityId);
 }
 
 IOutputRowDeserializer *COutputMetaData::createDiskDeserializer(ICodeContext * ctx, unsigned activityId)