gltf_viewer doesn't like being launched many times rapidly

An interesting stress test is to run this command on Android:
`adb shell am start -W -R 200 -n com.google.android.filament.gltf/.MainActivity`

This will launch gltf_viewer 200 times. Ideally this should work without any problem, but in practice the app crashes or hangs for various reasons. The hello_triangle test for instance works well.
Here is an example of problem it ran into:

```
2021-07-16 11:15:03.035 9894-9894/com.google.android.filament.gltf E/civetweb: cannot bind to 8082: 98 (Address already in use)
2021-07-16 11:15:03.035 9894-9894/com.google.android.filament.gltf E/Filament: Unable to start RemoteServer, see civetweb.txt for details.
2021-07-16 11:15:03.037 9894-9894/com.google.android.filament.gltf E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.google.android.filament.gltf, PID: 9894
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.google.android.filament.gltf/com.google.android.filament.gltf.MainActivity}: java.lang.IllegalStateException: Couldn't create RemoteServer
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3431)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7660)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.IllegalStateException: Couldn't create RemoteServer
at com.google.android.filament.utils.RemoteServer.(RemoteServer.java:43)
at com.google.android.filament.gltf.MainActivity.onCreate(MainActivity.kt:110)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3404)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:223) 
at android.app.ActivityThread.main(ActivityThread.java:7660) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
```