pull: When mirroring, only replace summary if we're doing a full mirror

We're hitting this in flathub, where we have a bunch of local builds,
but we also mirror a few refs from the gnome runtime repo into it.
Its fixable by re-doing the summary, but for a short time the
wrong version is visible.

Fixes https://github.com/ostreedev/ostree/issues/846

Closes: #935
Approved by: cgwalters

src/libostree/ostree-repo-pull.c

@@ -3518,7 +3518,7 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
         }
     }
 
-  if (pull_data->is_mirror && pull_data->summary_data)
+  if (pull_data->is_mirror && pull_data->summary_data && !refs_to_fetch && !configured_branches)
     {
       GLnxFileReplaceFlags replaceflag =
         pull_data->repo->disable_fsync ? GLNX_FILE_REPLACE_NODATASYNC : 0;