Call plugin unload function after stopping event loop (#539)

This can prevent race conditions where unload is clearing data but main is still working with it

backend/src/plugin.py

@@ -118,11 +118,11 @@ class PluginWrapper:
 
         if "stop" in data:
             self.log.info("Calling Loader unload function.")
-            await self._unload()
             get_event_loop().stop()
             while get_event_loop().is_running():
                 await sleep(0)
             get_event_loop().close()
+            await self._unload()
             raise Exception("Closing message listener")
 
         # TODO there is definitely a better way to type this