Fix #741: ValueError in WordSwapChangeNumber._alter_number for negative numbers

- Ensure change is always positive: change = abs(int(num * max_change)) + 1
- This fixes the issue where negative numbers could produce invalid ranges
- Maintains exact same behavior for all valid inputs
- Minimal change to avoid breaking existing tests

Fixes #741

Author: OpenClaw Assistant

textattack/transformations/word_swaps/word_swap_change_number.py

@@ -104,7 +104,8 @@ def _alter_number(self, num):
         """Helper function of _get_new_number, replace a number with another
         random number within the range of self.max_change."""
         if num not in [0, 2, 4]:
-            change = int(num * self.max_change) + 1
+            # Ensure change is always positive to avoid invalid ranges
+            change = abs(int(num * self.max_change)) + 1
             if num >= 0:
                 num_list = np.random.randint(max(num - change, 1), num + change, self.n)
             else: