Issue with shader terrain

Hi,

I encounter some issues with the shader terrain in 1.10. For my setup I create and destroy ShaderTerrainMesh instances to switch height maps. It seems that if I ever generate a ShaderTerrainMesh instance with a height map file that has already been used to generate any ShaderTerrainMesh instance, panda freezes or crashes (Sample program crashes, my own project freezes).

I tried model-cache-textures #f in the config but it didn’t help.

I clean up a ShaderTerrainMesh instance for the sample program with:

self.terrain_node = None
self.terrain.removeNode()
self.terrain = None