ostree/dump: Fix a memory leak

Re-using the `refs` variable for the main list of refs, plus the
iterated lists, meant that the main list was never freed (although all
the iterated ones were freed correctly).

Fix this by using two variables rather than reusing the one.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

src/ostree/ot-dump.c

@@ -322,10 +322,11 @@ ot_dump_summary_bytes (GBytes          *summary_bytes,
   collection_map = g_variant_lookup_value (exts, OSTREE_SUMMARY_COLLECTION_MAP, G_VARIANT_TYPE ("a{sa(s(taya{sv}))}"));
   if (collection_map != NULL)
     {
+      g_autoptr(GVariant) collection_refs = NULL;
       g_variant_iter_init (&iter, collection_map);
 
-      while (g_variant_iter_loop (&iter, "{&s@a(s(taya{sv}))}", &collection_id, &refs))
-        dump_summary_refs (collection_id, refs);
+      while (g_variant_iter_loop (&iter, "{&s@a(s(taya{sv}))}", &collection_id, &collection_refs))
+        dump_summary_refs (collection_id, collection_refs);
     }
 
   /* Print out the additional metadata. */