BUG: Fix auxdata initialization in ufunc slow path

The reason this was not found earlier is that auxdata is currently
set by most function and the fast path seems to be taken a shocking
amount of times.
There are no further similar missing inits.

Closes numpygh-28117

Author: seberg

numpy/_core/src/umath/ufunc_object.c

@@ -1108,7 +1108,7 @@ execute_ufunc_loop(PyArrayMethod_Context *context, int masked,
      * based on the fixed strides.
      */
     PyArrayMethod_StridedLoop *strided_loop;
-    NpyAuxData *auxdata;
+    NpyAuxData *auxdata = NULL;
     npy_intp fixed_strides[NPY_MAXARGS];
 
     NpyIter_GetInnerFixedStrideArray(iter, fixed_strides);

numpy/_core/tests/test_nep50_promotions.py

@@ -237,6 +237,20 @@ def test_integer_comparison(sctype, other_val, comp):
     assert_array_equal(comp(other_val, val_obj), comp(other_val, val))
 
 
+@pytest.mark.parametrize("arr", [
+    np.ones((100, 100), dtype=np.uint8)[::2],  # not trivially iterable
+    np.ones(20000, dtype=">u4"),  # cast and >buffersize
+    np.ones(100, dtype=">u4"),  # fast path compatible with cast
+])
+def test_integer_comparison_with_cast(arr):
+    # Similar to above, but mainly test a few cases that cover the slow path
+    # the test is limited to unsigned ints and -1 for simplicity.
+    res = arr >= -1
+    assert_array_equal(res, np.ones_like(arr, dtype=bool))
+    res = arr < -1
+    assert_array_equal(res, np.zeros_like(arr, dtype=bool))
+
+
 @pytest.mark.parametrize("comp",
         [np.equal, np.not_equal, np.less_equal, np.less,
          np.greater_equal, np.greater])