Fortran: Fix some minor PDT parse errors [PR95543,PR103748]

Fortran: Fix some minor PDT parse errors [PR95543,PR103748]

2025-10-12  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/95543
	PR fortran/103748
	* decl.cc (insert_parameter_exprs): Guard param->expr before
	using it.
	(gfc_get_pdt_instance): Substitute paramaters in kind default
	initializers.
	(gfc_match_decl_type_spec): Emit an error if a type paramter
	specification list appears in a variable declaraion with a
	non-parameterized type.
	* primary.cc (gfc_match_rvalue): Emit an error if a type spec
	list is empty.

gcc/testsuite/
	PR fortran/95543
	* gfortran.dg/pdt_17.f03: Change error message.
	* gfortran.dg/pdt_57.f03: New test.

	PR fortran/103748
	* gfortran.dg/pdt_58.f03: New test.