Exception when trying to print a result of FRED as NIF output

## Problem

For some datasets, the result of FRED can not be printed as NIF file (e.g., for further analysis) because the printing crashes.
```
2017-08-14 17:35:13,600 [pool-1-thread-1] ERROR [org.aksw.gerbil.execute.AnnotatorOutputWriter] -
java.lang.IndexOutOfBoundsException
at java.lang.String.codePointCount(String.java:733)
at org.aksw.gerbil.io.nif.AnnotationWriter.addSpan(AnnotationWriter.java:72)
at org.aksw.gerbil.io.nif.DocumentWriter.writeDocumentToModel(DocumentWriter.java:67)
at org.aksw.gerbil.io.nif.DocumentListWriter.writeDocumentsToModel(DocumentListWriter.java:39)
at org.aksw.gerbil.io.nif.AbstractNIFWriter.createNIFModel(AbstractNIFWriter.java:42)
at org.aksw.gerbil.io.nif.AbstractNIFWriter.writeNIF(AbstractNIFWriter.java:60)
at org.aksw.gerbil.execute.AnnotatorOutputWriter.storeAnnotatorOutput(AnnotatorOutputWriter.java:63)
at org.aksw.gerbil.execute.ExperimentTask.runExperiment(ExperimentTask.java:398)
at org.aksw.gerbil.execute.ExperimentTask.run(ExperimentTask.java:136)
at org.aksw.simba.topicmodeling.concurrent.workers.WorkerImpl.run(WorkerImpl.java:44)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
```
It seems like FRED has created an annotation with a position that exceeds the length of the original text String.

## Solution
The writing of annotations should be able to handle such a problem, e.g., by logging the problem but still writing the annotation.