In REPL `dis.distb()` raise AttributeError when the previous input fails to compile

Bug report

Bug description:

in REPL input following sequentially

1. import dis
2. some invalid code
3. dis.distb()

>>> import dis
>>> ??? 
  File "<stdin>", line 1
    ???
    ^
SyntaxError: invalid syntax
>>> dis.distb()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    dis.distb()
    ~~~~~~~~~^^
  File "/home/dev/cpython/Lib/dis.py", line 150, in distb
    while tb.tb_next: tb = tb.tb_next
          ^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'tb_next'

It looks like dis.distb() doesn’t handle the case where the previous exception’s traceback could be None in the REPL.

CPython versions tested on:

3.14, CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-148317

從 Lib/dis.py 中 dis.distb() 附近的第 150 行開始，重現回報的 REPL 序列：import dis，輸入無效程式碼，然後呼叫 dis.distb()。在前面的編譯失敗之後，最終指令不再引發 AttributeError 即表示完成；開始前檢查連結的 gh-148317 工作。