fix(shift_monitors): grimblastVD monitor removed error (#178)

* fix(shift_monitors): grimblastVD monitor removed error

Resolves #161 in the same way as a519b80, but for the `shift_monitors` plugin

* fixes from run

Author: John-Paul-R

pyprland/plugins/shift_monitors.py

@@ -28,4 +28,7 @@ async def event_monitoradded(self, monitor: str) -> None:
 
     async def event_monitorremoved(self, monitor: str) -> None:
         """Keep track of monitors."""
-        self.monitors.remove(monitor)
+        try:
+            self.monitors.remove(monitor)
+        except ValueError:
+            self.log.warning("Monitor %s not found in state - can't be removed", monitor)