PR fortran/88379 - ICE with allocatable coarray, class and associate

Catch NULL pointer dereference for ASSOCIATE on allocatable coarray variable.

gcc/fortran/
	PR fortran/88379
	* resolve.c (resolve_assoc_var): Avoid NULL pointer dereference.

(cherry picked from commit 267f84c6035c9380c8d1e9cb83ffe299c23e3a85)

gcc/fortran/resolve.c

@@ -9048,7 +9048,7 @@ resolve_assoc_var (gfc_symbol* sym, bool resolve_target)
 	  as = NULL;
 	  sym->ts = *ts;
 	  sym->ts.type = BT_CLASS;
-	  attr = CLASS_DATA (sym)->attr;
+	  attr = CLASS_DATA (sym) ? CLASS_DATA (sym)->attr : sym->attr;
 	  attr.class_ok = 0;
 	  attr.associate_var = 1;
 	  attr.dimension = attr.codimension = 0;

gcc/testsuite/gfortran.dg/pr88379.f90

+! { dg-do compile }
+! { dg-options "-fcoarray=single" }
+! PR fortran/88379 - ICE with allocatable coarray, class and associate
+
+program p
+  type t
+  end type t
+  class(t), allocatable :: x[:]
+  associate (y => x)
+  end associate
+end