[qtdeclarative] Ensure that ShaderEffectSource's texture has correct parameters.

The provider is created on demand in textureProvider(), but its
parameters are set in updatePaintNode() so if updatePaintNode() was
called before a consumer asked for the texture provider, they wouldn't
be set until the next time updatePaintNode() was called.

Change-Id: Iff866d50a8fe16f3d371cb8e590528f5f8c5ee61