Trac #33966: KnotInfo interface returns wrong braid_notation for the unknot

The original database does not provide a value for the `braid_notation`
of the unknot. Thus this value has been set individually in the
interface, but unfortunately this value corresponds to a disjoint union
of two unknots. This bug remained unnoticed because the construction of
a link from a braid in Sage erases all additional unknots.

URL: https://trac.sagemath.org/33966
Reported by: soehms
Ticket author(s): Sebastian Oehms
Reviewer(s): Travis Scrimshaw

Author: Release Manager

src/sage/knots/knotinfo.py

@@ -611,14 +611,21 @@ def braid_notation(self, original=False):
             '{3, {-2, -2, -1, 2, -1}}'
             sage: L[L.items.braid_notation_old]
             '{4, {1, -2, 3, -2, -1, -2, -3, -2}}'
+
+        TESTS:
+
+        Check that :trac:`33966` is fixed::
+
+            sage: KnotInfo.K0_1.braid_notation()
+            (1,)
         """
         braid_notation = self[self.items.braid_notation]
         if original:
             return braid_notation
 
         if not braid_notation:
             # don't forget the unknot
-            return (1, -1)
+            return (1, )
 
         braid_notation = eval_knotinfo(braid_notation)
         if type(braid_notation) is list: