One of Florida’s largest grocers is reportedly on the brink of bankruptcy, potentially leaving retail landlords throughout the Southeast with massive empty anchor boxes at a time when most retailers are shrinking their physical footprints. Southeastern Grocers LLC — the Jacksonville-based parent company of Winn-Dixie — has been asking landlords in recent months to lower its lease payments, which is often a sign that a company is struggling, real estate sources in Tampa, Orlando and Jacksonville…