make index is broken

Hi! My port tree is on commit 9c85fa7 and my FreeBSD version is
13.1-RELEASE. It seems that after recent changes to the ports (moving of
WWW entries to Makefiles) `make index` has become broken.

Here are the last lines of `make index`:
--- describe.www ---
--- describe.x11 ---
--- describe.x11-clocks ---
--- describe.x11-drivers ---
--- describe.x11-fm ---
--- describe.x11-fonts ---
--- describe.x11-servers ---
--- describe.x11-themes ---
--- describe.x11-toolkits ---
--- describe.x11-wm ---
sort: Illegal byte sequence
 Done.

The empty index is produced. Do you know how to fix it? Should I also file
a PR?