The astronomical rally in GameStop has imposed huge losses of nearly $20 billion for short sellers this month, but they are not budging. Short-selling hedge funds have suffered a mark-to-market loss of $19.75 billion year to date in the brick-and-mortar video game retailer, including a nearly $8 billion loss on Friday as the stock kept ripping higher, according to data from S3 Partners. Still, short sellers mostly are holding onto their bearish positions or they are being replaced by new hedge funds willing to bet against the stock. GameStop shares that have been borrowed and sold short have declined by...