Fortran: avoid NULL pointer dereferences

Fortran: avoid NULL pointer dereferences

CLASS(), PARAMETER is not yet properly implemented in gfortran.  Using it
in declarations could lead to subsequent NULL pointer dereferences during
checking or simplification of expressions involving those CLASS variables.

gcc/fortran/ChangeLog:

	PR fortran/103137
	PR fortran/103138
	* check.c (gfc_check_shape): Avoid NULL pointer dereference on
	missing ref.
	* simplify.c (gfc_simplify_cshift): Avoid NULL pointer dereference
	when shape not set.
	(gfc_simplify_transpose): Likewise.