fixed error when a document is being loaded (balloons source object are not available yet)

ahb_techdraw_extensions.py

@@ -521,14 +521,15 @@ class TechDrawExtensions:
 		obj = self.getBalloonSourcePart(balloon)
 		path = self.getBalloonSourcePartPath(balloon)
 		
-		partDisplayName = 'Inconnu' if obj is None else self.getPartDisplayName(obj)
-		
+		if obj is not None:
 			objectCenterView = workbench.techDrawExtensions.computePartCenter(view, obj, path)
 		
 			balloon.OriginX = objectCenterView.x + balloon.Assembly_handbook_OriginOffsetX
 			balloon.OriginY = objectCenterView.y + balloon.Assembly_handbook_OriginOffsetY
 			
+			partDisplayName = 'Inconnu' if obj is None else self.getPartDisplayName(obj)
 			balloon.Text = partDisplayName
+		
 		balloon.ViewObject.Font = 'DejaVu Sans'
 		balloon.ViewObject.Fontsize = 4
 		balloon.BubbleShape = 'Inspection'