get_ref_dir(): return early if directory cannot be read

diff --git a/t/t4020-diff-external.sh b/t/t4020-diff-external.sh
index a7602cf923d95a51643753ce44fa65cf406aba9c..083f62d1d6bb6bfd908b0a03db1a47f80071ef91 100755 (executable)
--- a/t/t4020-diff-external.sh
+++ b/t/t4020-diff-external.sh
@@ -4,8 +4,6 @@ test_description='external diff interface test'
 
 . ./test-lib.sh
 
-_z40=0000000000000000000000000000000000000000
-
 test_expect_success setup '
 
        test_tick &&