Revert change to advanced

Author: AZero13

Sources/FoundationEssentials/FileManager/FileManager+Files.swift

@@ -542,7 +542,7 @@ extension _FileManagerImpl {
 
         var extendedAttrs: [String : Data] = [:]
         var current = keyList.baseAddress!
-        let end = keyList.baseAddress!.advanced(by: size)
+        let end = keyList.baseAddress!.advanced(by: keyList.count)
         while current < end {
             let currentKey = String(cString: current)
             defer { current = current.advanced(by: currentKey.utf8.count) + 1 /* pass null byte */ }