[Bug] Crash when switching themes

[sblatz]

When I try to switch to a new theme, the app crashes:

 Process: org.mozilla.fenix.debug, PID: 24193
    java.lang.NullPointerException: Attempt to invoke interface method 'boolean androidx.preference.Preference$OnPreferenceChangeListener.onPreferenceChange(androidx.preference.Preference, java.lang.Object)' on a null object reference
        at org.mozilla.fenix.settings.RadioButtonPreference.updateRadioValue(RadioButtonPreference.kt:100)
        at org.mozilla.fenix.settings.RadioButtonPreference.access$updateRadioValue(RadioButtonPreference.kt:20)
        at org.mozilla.fenix.settings.RadioButtonPreference$onBindViewHolder$1.onPreferenceClick(RadioButtonPreference.kt:87)
        at androidx.preference.Preference.performClick(Preference.java:1184)
        at androidx.preference.Preference.performClick(Preference.java:1166)
        at androidx.preference.Preference$1.onClick(Preference.java:181)
        at android.view.View.performClick(View.java:7333)
        at android.view.View.performClickInternal(View.java:7299)
        at android.view.View.access$3200(View.java:846)
        at android.view.View$PerformClick.run(View.java:27773)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)

┆Issue is synchronized with this Jira Task