Fortran: avoid NULL pointer dereference checking elemental procedure args

gcc/fortran/ChangeLog:

	PR fortran/104571
	* resolve.cc (resolve_elemental_actual): Avoid NULL pointer
	dereference.

gcc/testsuite/ChangeLog:

	PR fortran/104571
	* gfortran.dg/pr104571.f90: New test.

Co-authored-by: Steven G. Kargl <kargl@gcc.gnu.org>