Guard against screenshot capture failure

Summary:
Bit off an odd one but according to the crash report in T107008330,
the screenshot can sometimes be not a real buffer. This may not actually
fix things but should give us some more insights into what's up.

Changelog: Better handling of screenshot taking in navigation

Reviewed By: mweststrate

Differential Revision: D32797863

fbshipit-source-id: 6d16ccb82fb8258591f9bc5f79c00811b18b9c51

desktop/plugins/public/navigation/plugin.tsx

@@ -74,6 +74,12 @@ export function plugin(client: PluginClient<Events, Methods>) {
     });
 
     const screenshot: Buffer = await client.device.screenshot();
+    if (screenshot.byteLength === 0) {
+      console.warn(
+        '[navigation] Could not retrieve valid screenshot from the device.',
+      );
+      return;
+    }
     const blobURL = URL.createObjectURL(bufferToBlob(screenshot));
     // this process is async, make sure we update the correct one..
     const navigationEventIndex = navigationEvents