Fix crash in TorAndroidIntegration.handleMessage()

🐞 Bug Report

The Google Play console reports a +1.41% crashes spike since 15.0a2 release one week ago.

Main culprit on our side has this stack trace:

Exception java.util.ConcurrentModificationException:
  at java.util.HashMap$HashIterator.nextNode (HashMap.java:1603)
  at java.util.HashMap$KeyIterator.next (HashMap.java:1626)
  at org.mozilla.geckoview.TorAndroidIntegration.handleMessage (TorAndroidIntegration.java:177)
  at org.mozilla.gecko.EventDispatcher$3.run (EventDispatcher.java:13)
  at android.os.Handler.handleCallback (Handler.java:938)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at android.os.Looper.loopOnce (Looper.java:201)
  at android.os.Looper.loop (Looper.java:288)
  at android.app.ActivityThread.main (ActivityThread.java:7880)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:568)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1045)

Reproduction steps

Expected behaviour

Actual behaviour

Bookkeeping

• Browser version: 15.0a2
• Browser channel:
  • Release
  • Alpha
  • Nightly
• Distribution method:
  • Installer/archive from torproject.org
  • tor-browser-launcher
  • homebrew
  • Google Play
• Operating System:
  • Windows
  • macOS
  • Linux
  • Android
  • Tails
  • Other (please specify):
• Operating System Version:

Browser UI language

Have you modified any of the settings in about:preferences or about:config? If yes, which ones?

Do you have any extra extensions installed?

Troubleshooting

Does this bug occur in a fresh installation?

Is this bug new? If it is a regression, in which version of the browser did this bug first appear?

Does this bug occur in the Alpha release channel?

Does this bug occur in Firefox ESR (Desktop only)?

Does this bug occur in Firefox Rapid Release?

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