> I think I fixed this now on master.  Please have a look.

Unfortunately the fix broke builds configured with
--enable-gcc-warnings, as GCC complains about the use of an
uninitialized variable that appears to be a typo in the fix. I installed
the attached patch to unbreak the build; please check it to make sure
that I understood the intent of the fix correctly.

It's a good idea to use './configure --enable-gcc-warnings' when making
changes to the C code in Emacs, as GCC is reasonably good at catching
typos like this, and typically does not generate too many false alarms.