Handle `ZeroDivisionError` in feature evaluation

[Alex Van Mechelen]

Possible enhancement

Make the default feature value -1 when a ZeroDivisionError occurs for ratio features. Another value can be chosen if we want to distinguish this error from others leading to a -1 feature value.

Example

[WARNING] Bad expression: len(binary['cfg']['mal_used_apis']) / len(binary['cfg']['used_apis'])
00:00:06.524 [ERROR] division by zero
Traceback (most recent call last):
  File "/home/user/.local/lib/python3.11/site-packages/pbox/helpers/items.py", line 89, in _exec
    r = eval2(expr, d, {}, whitelist_nodes=WL_NODES + _WL_EXTRA_NODES)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/tinyscript/helpers/expressions.py", line 122, in eval2
    return __eval(expression, globals, locals, blacklist_builtins, whitelist_nodes)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/tinyscript/helpers/expressions.py", line 58, in __eval
    return eval(expr, globals, locals)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<string>", line 1, in <module>
ZeroDivisionError: division by zero

I tried solving the ZeroDivisionError issue in the feature definition by adding if binary['cfg']['used_apis'] else -1, but that didn't work. And then I figured it might be interesting to handle this error by default instead of doing it feature per feature.

[Alex]

@AlexVanMechelen See PR #123 ; this will allow to set None for undefined feature values without breaking features computation process.