fix size accounting for encrypted/compressed objects (#9690)

size calculation in crawler was using the real size
of the object instead of its actual size i.e either
a decrypted or uncompressed size.

this is needed to make sure all other accounting
such as bucket quota and mcs UI to display the
correct values.

cmd/posix.go

@@ -383,7 +383,15 @@ func (s *posix) CrawlAndGetDataUsage(ctx context.Context, cache dataUsageCache)
 			return 0, nil
 		}
 
-		return meta.Stat.Size, nil
+		// we don't necessarily care about the names
+		// of bucket and object, only interested in size.
+		// so use some dummy names.
+		size, err := meta.ToObjectInfo("dummy", "dummy").GetActualSize()
+		if err != nil {
+			return 0, errSkipFile
+		}
+		return size, nil
+
 	})
 	if err != nil {
 		return dataUsageInfo, err