Fix UI errors with not unset active library id after disabling editing

It lead to UI errors when library was removed and Bonsai was still trying to get it from active_library_id.

src/bonsai/bonsai/core/library.py

@@ -41,6 +41,7 @@ def enable_editing_library_references(library_tool: tool.Library, library: ifcop
 
 def disable_editing_library_references(library: tool.Library) -> None:
     library.clear_editing_mode()
+    library.set_active_library(None)
 
 
 def enable_editing_library(library: tool.Library) -> None:

src/bonsai/bonsai/tool/library.py

@@ -73,8 +73,12 @@ class Library(bonsai.core.tool.Library):
             new.name = reference.Name or "Unnamed"
 
     @classmethod
-    def set_active_library(cls, library: ifcopenshell.entity_instance) -> None:
-        bpy.context.scene.BIMLibraryProperties.active_library_id = library.id()
+    def set_active_library(cls, library: Union[ifcopenshell.entity_instance, None]) -> None:
+        props = bpy.context.scene.BIMLibraryProperties
+        if library is None:
+            props.active_library_id = 0
+        else:
+            props.active_library_id = library.id()
 
     @classmethod
     def set_active_reference(cls, reference: ifcopenshell.entity_instance) -> None: