[JENKINS-21224] Defend against exceptions in listeners, for now just for ItemListener.

java.lang.RuntimeException: Unable to copy /…/jobs/…/config.xml
	at hudson.plugins.jobConfigHistory.FileHistoryDao.createNewHistoryEntryAndCopyConfig(FileHistoryDao.java:252)
	at hudson.plugins.jobConfigHistory.FileHistoryDao.createNewItem(FileHistoryDao.java:238)
	at hudson.plugins.jobConfigHistory.JobConfigHistoryJobListener.onCreated(JobConfigHistoryJobListener.java:31)
	at hudson.model.listeners.ItemListener.fireOnCreated(ItemListener.java:161)
	at jenkins.model.Jenkins.putItem(Jenkins.java:2483)
	at …
Caused by: java.io.FileNotFoundException: /…/jobs/…/config.xml (No such file or directory)
	at java.io.FileInputStream.open(Native Method)
	at java.io.FileInputStream.<init>(FileInputStream.java:120)
	at hudson.plugins.jobConfigHistory.FileHistoryDao.copyConfigFile(FileHistoryDao.java:178)
	at hudson.plugins.jobConfigHistory.FileHistoryDao.createNewHistoryEntryAndCopyConfig(FileHistoryDao.java:250)
	... 108 more