[yambar] Fix bug in sway.py if no workspaces in use

yambar/sway.py

@@ -50,6 +50,7 @@ def subscribe(types: List[str]):
 def format_workspaces(workspaces):
 	result = []
 	last_output = None
+	i = 0
 	for i, ws in enumerate(sorted(
 			workspaces,
 			key=lambda x: ("" if x["output"] == "eDP-1" else x["output"], x["num"], x["name"])