Fixed re-enabling a still selected plugin

Summary: While testing manually discovered the sandy plugin infra din't cover the case that a plugin can be selected but not enabled at the same time. Added test and fixed that.

Reviewed By: nikoant

Differential Revision: D22308597

fbshipit-source-id: 6cef2b543013ee81cee449396d523dd9a657ad1c

desktop/app/src/test-utils/createMockFlipperWithPlugin.tsx

@@ -137,6 +137,7 @@ export async function createMockFlipperWithPlugin(
           );
       }
     };
+    client.rawSend = jest.fn();
 
     // enable the plugin
     if (