Nuke the metadata file if magic blob is wrong

Gbp-Pq: Name metadata-nuke-junk-data.patch

metadata/metatree.c

@@ -451,7 +451,15 @@ meta_tree_init (MetaTree *tree)
   if (memcmp (tree->header->magic, MAGIC, MAGIC_LEN) != 0)
     {
       g_warning ("can't init metadata tree %s: wrong magic", tree->filename);
-      goto err;
+      if (!tree->for_write)
+        goto err;
+
+      meta_tree_clear (tree);
+
+      if (g_unlink (tree->filename) != 0)
+        goto err;
+
+      goto retry;
     }
 
   if (tree->header->major != MAJOR_VERSION)