gh-35700: Fix corner case of ordered set partitions iteration
    
### 📚 Description

The function `multiset_permutation_next_lex` was wrong on empty input
and is fixed in this PR.

Fixes #35654

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.
    
URL: #35700
Reported by: Vincent Delecroix
Reviewer(s): Frédéric Chapoton

Author: Release Manager

src/sage/combinat/set_partition_ordered.py

@@ -1114,6 +1114,13 @@ def __iter__(self):
              [{1, 3}, {2}],
              [{2, 3}, {1}],
              [{1, 2, 3}]]
+
+        TESTS:
+
+        Test for :issue:`35654`::
+
+            sage: OrderedSetPartitions(set(),[0,0,0]).list()
+            [[{}, {}, {}]]
         """
         for x in Compositions(len(self._set)):
             for z in OrderedSetPartitions(self._set, x):
@@ -1379,11 +1386,18 @@ def multiset_permutation_next_lex(l):
         [2, 1, 0, 0, 1]
         [2, 1, 0, 1, 0]
         [2, 1, 1, 0, 0]
+
+    TESTS:
+
+    Test for :issue:`35654`::
+
+        sage: multiset_permutation_next_lex([])
+        0
     """
     i = len(l) - 2
     while i >= 0 and l[i] >= l[i + 1]:
         i -= 1
-    if i == -1:
+    if i <= -1:
         return 0
     j = len(l) - 1
     while l[j] <= l[i]: