Horizontal section variable crash fix

The horizontal cross section would sometimes crash when adding a 2D variable, due to a texture not being initialized correctly. This was caused by the data pipeline for these variables, where 2 data request were emitted, but both would have to be completed before the texture would be initialized. The first request is emitted, when the variable is initialized, while the second comes from the actor, to synchronize the variable with the sync control. However, the hasData() method would already return true after the first request, as expected. This sometimes caused the rendering of the variable to happen before the second request was processed, resulting in the crash. The texture is now checked, and the calculation only proceeds if it is valid, otherwise the variable is skipped until ready.