2+2=3, since we merge extra fields in central and local headers
if they are the same.

regress/extra_count_ignore_zip64.test

diff --git a/regress/extra_count_ignore_zip64.test b/regress/extra_count_ignore_zip64.test
index 53ae78e..e5f07a4 100644
--- a/regress/extra_count_ignore_zip64.test
+++ b/regress/extra_count_ignore_zip64.test
@@ -5,4 +5,4 @@
 file bigzero.zip bigzero.zip bigzero.zip
 stdout Extra field count: 2
 stdout Extra field count: 2
-stdout Extra field count: 4
+stdout Extra field count: 3