ev: fix ConcurrentModificationException in VehicleChargingHandler.notifyMobsimBeforeSimStep()

[michalmac]

Reported by Tobias Tietz:

java.util.ConcurrentModificationException: null
	at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1605) ~[?:?]
	at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1628) ~[?:?]
	at org.matsim.contrib.ev.charging.VehicleChargingHandler.notifyMobsimBeforeSimStep(VehicleChargingHandler.java:169) ~[classes/:?]
	at org.matsim.core.mobsim.qsim.MobsimListenerManager.fireQueueSimulationBeforeSimStepEvent(MobsimListenerManager.java:107) ~[classes/:?]
	at org.matsim.core.mobsim.qsim.QSim.doSimStep(QSim.java:390) ~[classes/:?]
	at org.matsim.core.mobsim.qsim.QSim.run(QSim.java:259) ~[classes/:?]
	at org.matsim.core.controler.NewControler.runMobSim(NewControler.java:125) ~[classes/:?]
	at org.matsim.core.controler.AbstractController$8.run(AbstractController.java:214) ~[classes/:?]
	at org.matsim.core.controler.AbstractController.iterationStep(AbstractController.java:246) ~[classes/:?]
	at org.matsim.core.controler.AbstractController.mobsim(AbstractController.java:210) ~[classes/:?]
	at org.matsim.core.controler.AbstractController.iteration(AbstractController.java:157) ~[classes/:?]
	at org.matsim.core.controler.AbstractController.doIterations(AbstractController.java:124) ~[classes/:?]
	at org.matsim.core.controler.AbstractController$1.run(AbstractController.java:84) ~[classes/:?]
	at org.matsim.core.controler.MatsimRuntimeModifications.run(MatsimRuntimeModifications.java:70) [classes/:?]
	at org.matsim.core.controler.MatsimRuntimeModifications.run(MatsimRuntimeModifications.java:53) [classes/:?]
	at org.matsim.core.controler.AbstractController.run(AbstractController.java:92) [classes/:?]
	at org.matsim.core.controler.NewControler.run(NewControler.java:83) [classes/:?]
	at org.matsim.core.controler.Controler.run(Controler.java:259) [classes/:?]
	at org.matsim.contrib.ev.eTruckTraffic.RunETruckTraffic.run(RunETruckTraffic.java:69) [classes/:?]
	at org.matsim.contrib.ev.eTruckTraffic.RunETruckTraffic.main(RunETruckTraffic.java:50) [classes/:?]