Loop in ProcessChangesAsync if an exception is thrown

## Problem ##
The watcher of our collections continue to produce the same output. We found that it was induced from the processing of the same documents over and over.
## Cause ##
One of the documents generate an exception during it transformations and all the documents weren't marked as elaborated. This means that overriding the method ProcessChangesAsync could introduce loop or freeze when an exception is thrown and not properly managed.
## Solution ##
We decided to catch the exception, log it and move on. At the moment this is not a problem for us but would be better to have another solution.

## Question ##
Are there better options to process the documents? For example an override of a methods that received only one of the documents. In this way the base class know exactly which document is processed and which not.

Example: If I found a document that broke my code I want to leave it there untouched until I release a new version of the code able to manage it properly.