opengl.texture_set.stream: Handle case where 'Animation_view' is null.

3-mid/opengl/source/lean/opengl-texture_set.adb

@@ -240,7 +240,13 @@ is
                     Item   : in              Animation_view)
    is
    begin
+      if Item = null
+      then
+         Boolean'write (Stream, False);
+      else
+         Boolean'write (Stream, True);
          Animation'output (Stream, Item.all);
+      end if;
    end write;
 
 
@@ -248,8 +254,16 @@ is
    procedure read (Stream : not null access Ada.Streams.Root_Stream_Type'Class;
                    Item   : out             Animation_view)
    is
+      Item_not_null : Boolean;
    begin
+      Boolean'read (Stream, Item_not_null);
+
+      if Item_not_null
+      then
          Item := new Animation' (Animation'Input (Stream));
+      else
+         Item := null;
+      end if;
    end read;