another plperl bug

I discovered a further plperl bug last night. If foo() is a SRF and
therefore returns an arrayref, calling select foo() rather than select *
from foo() causes a segfault because this line passes NULL as the argument:
   tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);

I am not sure I even know what the behaviour should be, and my available
time to work on a fix is severely contrained ATM.

cheers

andrew