Fix Coverity bug report

CID 173749: Uninitialized members (UNINIT_CTOR)
/c++/src/Reader.cc: 259 in orc::RowReaderImpl::RowReaderImpl(std::shared_ptr<orc::FileContents>, const orc::RowReaderOptions &)()
253 } else

{ 254 previousRow = firstRowOfStripe[firstStripe]-1; 255 }

256
257 ColumnSelector column_selector(contents.get());
258 column_selector.updateSelected(selectedColumns, options);
>>> CID 173749: Uninitialized members (UNINIT_CTOR)
>>> Non-static class member "rowsInCurrentStripe" is not initialized in this constructor nor in any functions that it calls.
259 }
260
261 const RowReaderOptions& RowReaderImpl::getRowReaderOptions() const

{ 262 return options; 263 }

264