eeschema: Fix undo stacking for break wire

The break wire command is actually two commands: modify the existing
wire and add a new wire.  This means that the command must append to the
previous commit to avoid breaking the undo stack

Fixes: lp:1824251
* https://bugs.launchpad.net/kicad/+bug/1824251

eeschema/bus-wire-junction.cpp

@@ -776,8 +776,8 @@ bool SCH_EDIT_FRAME::BreakSegment( SCH_LINE* aSegment, const wxPoint& aPoint,
     newSegment->SetStartPoint( aPoint );
     AddToScreen( newSegment, aScreen );
 
-    if( aAppend )
-        SaveCopyInUndoList( newSegment, UR_NEW, true );
+    SaveCopyInUndoList( newSegment, UR_NEW, aAppend );
+    SaveCopyInUndoList( aSegment, UR_CHANGED, true );
 
     RefreshItem( aSegment );
     aSegment->SetEndPoint( aPoint );