Fix fs.is_dir detection on the Mac, take 2

Thanks to @andyli for the report and pointer to the failing CI
build.

Fixes #104

1 files changed, 4 insertions, 1 deletions

diff --git a/src/luarocks/fs/unix.lua b/src/luarocks/fs/unix.lua
index eb7d870b..3e05fbf3 100644
--- a/src/luarocks/fs/unix.lua
+++ b/src/luarocks/fs/unix.lua
@@ -220,8 +220,11 @@ function unix.is_dir(file)
       return true
    end
    if fd then
+      local _, _, ecode = fd:read(1)
       fd:close()
-      return true
+      if ecode == 21 then -- "Is a directory"
+         return true
+      end
    end
    return false
 end