fix crash in ViewThreadFragment.removeItem

[connyduck]

from Google Play console

Exception java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
  at java.util.ArrayList.get (ArrayList.java:437)
  at java.util.Collections$UnmodifiableList.get (Collections.java:1356)
  at com.keylesspalace.tusky.components.viewthread.ViewThreadFragment.removeItem (ViewThreadFragment.kt:419)
  at com.keylesspalace.tusky.fragment.SFragment$showConfirmDeleteDialog$1$1.invokeSuspend (SFragment.kt:364)
  at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith (ContinuationImpl.kt:33)
  at kotlinx.coroutines.DispatchedTask.run (DispatchedTask.kt:106)
  at android.os.Handler.handleCallback (Handler.java:938)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at android.os.Looper.loopOnce (Looper.java:226)
  at android.os.Looper.loop (Looper.java:313)
  at android.app.ActivityThread.main (ActivityThread.java:8663)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:571)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1135)