Excelize: Panic in cellInRange on a worksheet with an empty mergeCell ref

Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.7.1 to 2.11.0, mergeCellsParser leaves the cached rectangle empty for an empty mergeCell ref and then passes that empty slice to cellInRange without a length check. GetCellValue reaches mergeCellsParser, which passes an empty rectangle derived from the mergeCell ref attribute into cellInRange. When a crafted worksheet contains an empty mergeCell ref and a non-streaming cell API reads the worksheet, cellInRange indexes four positions in an empty slice, allowing an attacker to panic on the first affected cell operation. No fixed version is available as of this review.