Define dummy 3DConnexion interface in case module is not available

CURA-12404

cura/NavlibClient.py

@@ -1,4 +1,3 @@
-import pynavlib.pynavlib_interface as pynav
 from UM.Math.Matrix import Matrix
 from UM.Math.Vector import Vector
 from UM.Math.AxisAlignedBox import AxisAlignedBox
@@ -6,6 +5,10 @@ from cura.PickingPass import PickingPass
 from UM.Scene.Iterator.DepthFirstIterator import DepthFirstIterator
 from cura.Scene.OverlayNode import OverlayNode, SceneNode
 from UM.Resources import Resources
+from UM.Logger import Logger
+
+try:
+    import pynavlib.pynavlib_interface as pynav
 
     class NavlibClient(pynav.NavlibNavigationModel):
 
@@ -262,3 +265,16 @@ class NavlibClient(pynav.NavlibNavigationModel):
             else:
                 self._scene.getRoot().removeChild(self._pivot_node)
         
+except BaseException as exception:
+    Logger.warning(f"Unable to load 3DConnexion library: {exception}")
+
+    # Define dummy class instead so that integration is transparent from outside
+    class NavlibClient:
+        def __init__(self, scene, renderer) -> None:
+            pass
+
+        def put_profile_hint(self, hint) -> None:
+            pass
+
+        def enable_navigation(self, enabled) -> None:
+            pass