ConcurrentModificationException in ISOMsg.dump

[chhil]

Jmeter with a ISO8583 sampler that uses jpos 2.1.4

I initially logged this at tilln/jmeter-iso8583#24 but seems to be a jpos issue.

java.util.ConcurrentModificationException: null
	at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1211) ~[?:1.8.0_152]
	at java.util.TreeMap$KeyIterator.next(TreeMap.java:1265) ~[?:1.8.0_152]
	at org.jpos.iso.ISOMsg.dump(ISOMsg.java:522) ~[jpos-2.1.4.jar:2.1.4]
	at nz.co.breakpoint.jmeter.iso8583.MessagePrinter.asString(MessagePrinter.java:19) ~[jmeter-iso8583-1.1.jar:?]
	at nz.co.breakpoint.jmeter.iso8583.ISO8583Sampler.sample(ISO8583Sampler.java:153) ~[jmeter-iso8583-1.1.jar:?]
	at org.apache.jmeter.threads.JMeterThread.doSampling(JMeterThread.java:627) ~[ApacheJMeter_core.jar:5.2.1]
	at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:551) ~[ApacheJMeter_core.jar:5.2.1]
	at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:490) [ApacheJMeter_core.jar:5.2.1]
	at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:257) [ApacheJMeter_core.jar:5.2.1]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_152]

[ar]

This problem seems to be related to JMeter's use (or re-use) of ISOMsgs.

We had a similar problem in issue #212 solved in 42f58b1. Perhaps we can use a similar technique in ISOMsg.dump.