Fix material animations with only a <texture-prop>

Fix material animations with only a <texture-prop>

On 8/31/07, K. Hoercher <wbhoer@gmail.com> wrote:
> > Some notes:
> > - I found that in order to make the example from model-howto.html work
> > ( starting at "To make a texture replaceable at runtime") one has to
> > specify a valid (i.e. loadable) <texture>  in the material animation.

The cause seems to be the condition in SGMaterialAnimation.cxx l.277
ignoring any texture update by the UpdateCallback (only there
<texture-prop> is looked at)  without an already existing stateSet.
That in turn will not be created with a <texture-prop> alone l. 379ff.

Unless I overlooked some compelling reason contradicting, I'd like to
suggest allowing for a stateSet to be created for those situations
too. I think that would match the behaviour of animation.cxx
(PRE_OSG_PLIB_20061029) and is imho the more expected and also
documented one.