(tar_sparse_init): Fix recent bugfixes: Initialize dumped_size to 0.

src/sparse.c

@@ -102,6 +102,7 @@ tar_sparse_member_p (struct tar_sparse_file *file)
 static bool
 tar_sparse_init (struct tar_sparse_file *file)
 {
+  file->dumped_size = 0;
   if (file->optab->init)
     return file->optab->init (file);
   return true;