Fix call to unsafeResize in StructColumnReader (#7461)

Summary:
Pull Request resolved: #7461

Ensure call to unsafeResize sets new rows to false in StructColumnReader.
When adding unsafeRowApi (D50577808) I missed setting one call to false instead of the default true.

Reviewed By: Yuhta

Differential Revision: D51091937

fbshipit-source-id: 441ed2b86d81fac6f703dd84f25a95b4e73752c7

velox/dwio/dwrf/reader/ColumnReader.cpp

@@ -1864,7 +1864,7 @@ void StructColumnReader::next(
     DWIO_ENSURE_GE(childrenVectors.size(), children_.size());
 
     // Resize rowVector
-    rowVector->unsafeResize(numValues);
+    rowVector->unsafeResize(numValues, false);
   }
 
   BufferPtr nulls = readNulls(numValues, result, incomingNulls);