Opening a second binary causes exceptions

### Description

```
ERROR | 2023-08-15 15:31:19,296 | angrmanagement.data.object_container | Error raised from event of (container: The current CFBlanket)None
Traceback (most recent call last):
File "/home/user/angr-management/angrmanagement/data/object_container.py", line 32, in am_event
listener(**kwargs)
File "/home/user/angr-management/angrmanagement/ui/views/disassembly_view.py", line 348, in _on_cfb_event
self._reload_current_function_if_changed()
File "/home/user/angr-management/angrmanagement/ui/views/disassembly_view.py", line 336, in _reload_current_function_if_changed
func = self.instance.kb.functions.get_by_addr(func_addr)
^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'functions'
ERROR | 2023-08-15 15:31:19,297 | angrmanagement.data.object_container | Error raised from event of (container: List of breakpoints)[]
Traceback (most recent call last):
File "/home/user/angr-management/angrmanagement/data/object_container.py", line 32, in am_event
listener(**kwargs)
File "/home/user/angr-management/angrmanagement/ui/views/disassembly_view.py", line 881, in _on_breakpoints_updated
self.refresh()
File "/home/user/angr-management/angrmanagement/ui/views/disassembly_view.py", line 161, in refresh
self._current_view.refresh()
File "/home/user/angr-management/angrmanagement/ui/widgets/qdisasm_graph.py", line 205, in refresh
b.refresh()
File "/home/user/angr-management/angrmanagement/ui/widgets/qblock.py", line 118, in refresh
obj.refresh()
File "/home/user/angr-management/angrmanagement/ui/widgets/qinstruction.py", line 132, in refresh
operand.refresh()
File "/home/user/angr-management/angrmanagement/ui/widgets/qoperand.py", line 161, in refresh
self._init_widgets()
File "/home/user/angr-management/angrmanagement/ui/widgets/qoperand.py", line 284, in _init_widgets
variable, offset = self._pick_variable(variable_and_offsets)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/user/angr-management/angrmanagement/ui/widgets/qoperand.py", line 444, in _pick_variable
arch = self.instance.project.arch
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/user/angr-management/angrmanagement/data/object_container.py", line 80, in __getattr__
return getattr(self._am_obj, item)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'arch'
```

### Steps to reproduce the bug

1. Open a binary
2. Open a different binary

### Environment

angr-management @ 750ac6cca697f1ced8c27c351211f132cd440d11

### Additional context

_No response_