Remember erroneous type when creating GENERIC for named type.

From-SVN: r169030

gcc/go/gofrontend/types.cc

@@ -7085,7 +7085,10 @@ Named_type::do_get_tree(Gogo* gogo)
       this->named_tree_ = t;
       t = this->type_->struct_type()->fill_in_tree(gogo, t);
       if (t == error_mark_node)
-	return error_mark_node;
+	{
+	  this->named_tree_ = error_mark_node;
+	  return error_mark_node;
+	}
       break;
 
     case TYPE_ARRAY:
@@ -7120,7 +7123,10 @@ Named_type::do_get_tree(Gogo* gogo)
 	  this->named_tree_ = t;
 	  t = this->type_->interface_type()->fill_in_tree(gogo, t);
 	  if (t == error_mark_node)
-	    return error_mark_node;
+	    {
+	      this->named_tree_ = error_mark_node;
+	      return error_mark_node;
+	    }
 	}
       break;