make sure that getField does not write after supplied buffer
    (recommit to correct clone, for easy merging)


ndb/include/util/Bitmask.hpp:
  ndb- bug#33750
        make sure that getField does not write after supplied buffer
ndb/src/common/util/Bitmask.cpp:
  ndb- bug#33750
        make sure that getField does not write after supplied buffer
ndb/test/ndbapi/testBitfield.cpp:
  move test from Bitmask.cpp into testBitfield
        for automatic testing