Reset active drawing id if we removed the active drawing

Previously there was an error if you remove all drawings:
```
Traceback (most recent call last):
  File "\addons\blenderbim\bim\module\drawing\ui.py", line 182, in draw
    DrawingsData.load()
  File "\addons\blenderbim\bim\module\drawing\data.py", line 106, in load
    "active_drawing_pset_data": cls.active_drawing_pset_data(),
  File "\addons\blenderbim\bim\module\drawing\data.py", line 134, in active_drawing_pset_data
    drawing = ifc_file.by_id(bpy.context.scene.DocProperties.active_drawing_id)
  File "\addons\blenderbim\libs\site\packages\ifcopenshell\file.py", line 326, in by_id
    return self[id]
  File "\addons\blenderbim\libs\site\packages\ifcopenshell\file.py", line 314, in __getitem__
    return entity_instance(self.wrapped_data.by_id(key), self)
  File "\addons\blenderbim\libs\site\packages\ifcopenshell\ifcopenshell_wrapper.py", line 4517, in by_id
    return _ifcopenshell_wrapper.file_by_id(self, id)
RuntimeError: Instance #1 077 not found
```

Author: Andrej730

src/blenderbim/blenderbim/bim/module/drawing/operator.py

@@ -1410,10 +1410,14 @@ def _execute(self, context):
             drawings = [tool.Ifc.get().by_id(self.drawing)]
 
         print("Removing drawings: {}".format([d for d in drawings]))
+        removed_drawings = [drawing.id() for drawing in drawings]
 
         for drawing in drawings:
             core.remove_drawing(tool.Ifc, tool.Drawing, drawing=drawing)
 
+        active_drawing_id = context.scene.DocProperties.active_drawing_id
+        if active_drawing_id in removed_drawings:
+            context.scene.DocProperties.active_drawing_id = 0
 
 class ReloadDrawingStyles(bpy.types.Operator):
     bl_idname = "bim.reload_drawing_styles"