Better handling of `RuntimeException`s in `ObjectGraphWalker`

[roytruelove]

(on version 0.2.0, using ehcache version 3.0.2)

I was getting the following WARN-level logs when attempting to cache a certain object:

Max Object Graph Size reached for the object

thrown from here.

In order to determine why I was getting this, I set the traversalDebugMessage to true (using the log levels and the system property) and I can see in a debugger that it's being appended to as it's being walked.

The issue is, if anything in the walk method throws a RuntimeException, the code that ultimately provides the message to the logger is never called.

This code should be wrapped in a finally clause to log the traversalDebugMessage. Without those logs it's difficult to debug errors like the one given above.

Thank you!