message: Fix a C++ error when deleting units
diff: @@ -141,9 +141,7 @@ def flipUnitsInCityAfter(tCityPlot, iPlayer):
  # used: RiseAndFall
  def killUnitsInArea(iPlayer, area):
  for plot in area:
  - killedUnits = units.at(plot).owner(iPlayer)
  - for unit in killedUnits:
  - unit.kill(False, -1)
  + killUnits(units.at(plot).owner(iPlayer))
  # used: RiseAndFall
  # TODO: accept a Plots instance instead of lPlots
  @@ -1146,7 +1144,7 @@ def flipOrCreateDefenders(iNewOwner, units, tPlot, iNumDefenders):
  # used: Congresses, Stability
  def killUnits(lUnits):
  - for unit in lUnits:
  + for unit in units.of(lUnits).where(lambda unit: not unit.isCargo()):
  if location(unit) >= (0, 0):
  unit.kill(False, barbarian())
  