fix broken backtrack edge generation

src/Mod/CAM/Path/Op/Vcarve.py

@@ -164,7 +164,7 @@ def generateVirtualBackTrackEdges(positionHistory, nextEdge, tolerance) -> list:
     to follow them without lifting toolbit. This approach makes carving a lot of faster.
     """
 
-    if not positionHistory:
+    if not positionHistory or len(positionHistory) < 2:
         return []
 
     backTrackEdges = []
@@ -591,6 +591,8 @@ class ObjectVcarve(PathEngraveBase.ObjectOp):
             # but using some routing logic we may avoid raising CNC toolbit and using G0
             # and instead traverse back already carved edges at full speed
 
+            backtrack_edges = generateVirtualBackTrackEdges(positionHistory, wire[0], obj.Tolerance)
+
             edge_list = backtrack_edges + wire
 
             e = edge_list[0]