Merge branch 'jk/misc-uninitialized-fixes'

Various fixes to codepaths gcc 9 had trouble following dataflow. * jk/misc-uninitialized-fixes: pack-objects: drop packlist index_pos optimization test-read-cache: drop namelen variable diff-delta: set size out-parameter to 0 for NULL delta bulk-checkin: zero-initialize hashfile_checkpoint pack-objects: use object_id in packlist_alloc() git-am: handle missing "author" when parsing commit