Fix AttributeError on self.width if Tesseract finds no OCR text

self.width remains undefined unless hOCR finds text.  It might not, if
a page contains only an image for example.

Full error message is:
AttributeError: ‘hocrTransform’ object has no attribute ‘width’
Merge pull request #56 from jbarlow83/for-upstream/hocr-selfwidth

Fix AttributeError on self.width if Tesseract finds no OCR text