remote-bzr: fix order of locking in CustomTree

diff --git a/contrib/remote-helpers/git-remote-bzr b/contrib/remote-helpers/git-remote-bzr
index 91b5cda7671f6a4169ce8ec02de987242ef5f9f5..b428244cac93c266f1118315503def6ffea1cf7a 100755 (executable)
--- a/contrib/remote-helpers/git-remote-bzr
+++ b/contrib/remote-helpers/git-remote-bzr
@@ -389,8 +389,8 @@ class CustomTree():
 
         def copy_tree(revid):
             files = files_cache[revid] = {}
-            tree = repo.repository.revision_tree(revid)
             repo.lock_read()
+            tree = repo.repository.revision_tree(revid)
             try:
                 for path, entry in tree.iter_entries_by_dir():
                     files[path] = entry.file_id