minor cleanup of merged pull request, add test

Cython/Utility/MemoryView.pyx

@@ -986,9 +986,11 @@ cdef memoryview_fromslice({{memviewslice_name}} memviewslice,
 
     result.view.shape = <Py_ssize_t *> result.from_slice.shape
     result.view.strides = <Py_ssize_t *> result.from_slice.strides
+
+    # only set suboffsets if actually used, otherwise set to NULL to improve compatibility
     result.view.suboffsets = NULL
-    for i in range(ndim):
-        if result.from_slice.suboffsets[i] >= 0:
+    for suboffset in result.from_slice.suboffsets[:ndim]:
+        if suboffset >= 0:
             result.view.suboffsets = <Py_ssize_t *> result.from_slice.suboffsets
             break
 

tests/memoryview/memoryview.pyx

@@ -1012,3 +1012,13 @@ def test_assignment_in_conditional_expression(bint left):
     c = a if left else b
     for i in range(c.shape[0]):
         print c[i]
+
+
+def test_cpython_offbyone_issue_23349():
+    """
+    >>> print(test_cpython_offbyone_issue_23349())
+    testing
+    """
+    cdef unsigned char[:] v = bytearray(b"testing")
+    # the following returns 'estingt' without the workaround
+    return bytearray(v).decode('ascii')