[ocrfeeder/introspection] Fix error when exporting a PDF with empty text areas

[Joaquim Manuel Pereira Rocha <jrocha src gnome org>]

commit 531b2f9078663228ffcb745ba56d998d88c567ec
Author: Joaquim Rocha <me joaquimrocha com>
Date:   Sun Jul 6 00:03:47 2014 +0200

    Fix error when exporting a PDF with empty text areas

 src/ocrfeeder/feeder/documentGeneration.py |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/ocrfeeder/feeder/documentGeneration.py b/src/ocrfeeder/feeder/documentGeneration.py
index 3c83796..9ff12a5 100644
--- a/src/ocrfeeder/feeder/documentGeneration.py
+++ b/src/ocrfeeder/feeder/documentGeneration.py
@@ -397,6 +397,8 @@ class PdfGenerator(DocumentGenerator):
         text.moveCursor(0, box.text_data.size)
         #todo: efficiently add the required font
         self.canvas.setFontSize(box.text_data.size)
+        if not box.text:
+            return
         lines = simpleSplit(box.text,
                             self.canvas._fontname,
                             box.text_data.size,