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

self.width remains undefined unless hOCR finds text. If there is <div class="ocr_page"> tag, which happens on occasion for some reason, then the Python script exits with an AttributeError instead of an error message, as apparently intended.

Error message is:
AttributeError: ‘hocrTransform’ object has no attribute ‘width’