Reviewer - OnRenderProcessGone Crash - You cannot show a dialog before an Activity is created or after it's hidden

https://couchdb.ankidroid.org/acralyzer/_design/acralyzer/index.html#/report-details/896af9d5-cb72-4c8e-8ba1-6e3e0f233819

```
com.afollestad.materialdialogs.MaterialDialog$DialogException: Bad window token, you cannot show a dialog before an Activity is created or after it's hidden.
at com.afollestad.materialdialogs.MaterialDialog.show(MaterialDialog.java:2)
at com.afollestad.materialdialogs.MaterialDialog$Builder.show(MaterialDialog.java:2)
at com.ichi2.anki.AbstractFlashcardViewer$CardViewerWebClient.displayRenderLoopDialog(AbstractFlashcardViewer.java:13)
at com.ichi2.anki.AbstractFlashcardViewer$CardViewerWebClient.onRenderProcessGone(AbstractFlashcardViewer.java:24)
at gk.a(PG:1)
at org.chromium.android_webview.AwContents.onRenderProcessGone(PG:9)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:326)
at android.os.Looper.loop(Looper.java:160)
at android.app.ActivityThread.main(ActivityThread.java:6898)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:537)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
```