Fixed uncaught exception on first run

cura/PlatformPhysics.py

@@ -48,7 +48,13 @@ class PlatformPhysics:
             bbox = node.getBoundingBox()
 
             # Ignore intersections with the bottom
-            build_volume_bounding_box = self._build_volume.getBoundingBox().set(bottom=-9001)
+            build_volume_bounding_box = self._build_volume.getBoundingBox()
+            if build_volume_bounding_box:
+                build_volume_bounding_box.set(bottom=-9001)
+            else:
+                # No bounding box. This is triggered when running Cura from command line with a model for the first time
+                # In that situation there is a model, but no machine (and therefore no build volume.
+                return
             node._outside_buildarea = False
 
             # Mark the node as outside the build volume if the bounding box test fails.