Added check against null colour layer to prevent a crash when a null colour layer is assigned

src/osgTerrain/GeometryTechnique.cpp

@@ -725,7 +725,7 @@ void GeometryTechnique::applyColorLayers()
             {
                 continue;
             }
-            
+
             colorLayer = switchLayer->getLayer(switchLayer->getActiveLayer());
             if (!colorLayer) continue;
         }
@@ -795,7 +795,7 @@ void GeometryTechnique::applyTransparency()
     bool containsTransparency = false;
     for(unsigned int i=0; i<_terrainTile->getNumColorLayers(); ++i)
     {
-        osg::Image* image = _terrainTile->getColorLayer(i)->getImage();
+        osg::Image* image = (_terrainTile->getColorLayer(i)!=0) ? _terrainTile->getColorLayer(i)->getImage() : 0;
         if (image)
         {
             containsTransparency = image->isImageTranslucent();