#135 Exception when exporting writing sheets

[bogleg]

This exception is seen when exporting to writing sheet format on certain word lists:
ExceptionConverter: java.io.IOException: The document has no pages.
at com.lowagie.text.pdf.PdfPages.writePageTree (Unknown Source)
at com.lowagie.text.pdf.PdfWriter.close(Unknown Source)
at com.lowagie.text.pdf.PdfDocument.close(Unknown Source)
at com.lowagie.text.Document.close(Unknown Source)
at net.sourceforge.zdt.flashcard.formats.WritingSheetFormat.exportEntries (WritingSheetFormat.java:172)
at net.sourceforge.zdt.flashcard.views.CategoryViewController.exportToFile(CategoryViewController.java:86)
at net.sourceforge.zdt.flashcard.views.CategoryView$18.run(CategoryView.java :754)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

[bogleg]

Logged In: YES
user_id=1223911
Originator: YES

Fix the exception but not the problem. When a problem occurs, it will skip the failed entry and keep going instead of dying.