TileByteStream+TrigT2CaloCommon: Fix uninitialized read in test.
Make sure the D0CellsHLT::cells array is initialized. Fixes test failure in dbg / clang builds. Also rename it to m_cells, for consistency with the other members of this structure.
Make sure the D0CellsHLT::cells array is initialized. Fixes test failure in dbg / clang builds. Also rename it to m_cells, for consistency with the other members of this structure.