Dear all,

the attached patch fixes issues with assignments of unlimited polymorphic
entities that were found with the help of valgrind or asan, see PR.  Looking
further into it, it turns out that allocation sizes as well as array spans
could be set incorrectly, leading to wrong results or heap corruption.

The fix is rather straightforward: take into the _len of unlimited
polymorphic entities when it is non-zero to get the correct allocation
sizes and array spans.

The patch has been tested by the reporter, see PR.

Regtested on x86_64-pc-linux-gnu.  OK for 15-mainline?

I would like to backport this to active branches where appropriate,
starting with 14 after it reopens after release.  Is this OK?

Thanks,
Harald