Updater: remove dialog before showing a new one and when detaching

2020-04-03 16:18:18.286 28742-28742/org.lineageos.updater E/WindowManager: android.view.WindowLeaked: Activity org.lineageos.updater.UpdatesActivity has leaked window DecorView@5dd12b3[UpdatesActivity] that was originally added here
        at android.view.ViewRootImpl.<init>(ViewRootImpl.java:621)
        at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:377)
        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:96)
        at android.app.Dialog.show(Dialog.java:342)
        at androidx.appcompat.app.AlertDialog$Builder.show(AlertDialog.java:1009)
        at org.lineageos.updater.UpdatesListAdapter.showInfoDialog(UpdatesListAdapter.java:552)
        at org.lineageos.updater.UpdatesListAdapter.lambda$setButtonAction$5$UpdatesListAdapter(UpdatesListAdapter.java:375)
        at org.lineageos.updater.-$$Lambda$UpdatesListAdapter$xtQzmsol8pO3BlYZkbKcb5gVAq4.onClick(Unknown Source:2)
        at org.lineageos.updater.UpdatesListAdapter.lambda$setButtonAction$9(UpdatesListAdapter.java:408)
        at org.lineageos.updater.-$$Lambda$UpdatesListAdapter$M4hRQyNgJseuHrw6EfkhK_yrGK8.onClick(Unknown Source:2)
        at android.view.View.performClick(View.java:7259)
        at android.view.View.performClickInternal(View.java:7236)
        at android.view.View.access$3600(View.java:801)
        at android.view.View$PerformClick.run(View.java:27896)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7397)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:491)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:935)

Change-Id: I7877b02b8526c7c12331a660a7ac934d02656e6f
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>