Fix segfault caused by table_index().
Fix segfault caused by table_index().

eddieantonio/isri-ocr-evaluation-tools,eddieantonio/ocreval,eddieantonio/isri-ocr-evaluation-tools,eddieantonio/isri-ocr-evaluation-tools,eddieantonio/ocreval,eddieantonio/ocreval