FATAL EXCEPTION on opening just shared image

Steps to reproduce:
1. Open galery, select image, share it with Element.
2. Tap this just shared image in Element.

```
D AndroidRuntime: Shutting down VM
E AndroidRuntime: FATAL EXCEPTION: main
E AndroidRuntime: Process: im.vector.app, PID: 6977
E AndroidRuntime: java.lang.ArrayIndexOutOfBoundsException: length=10; index=-1
E AndroidRuntime: at java.util.ArrayList.get(ArrayList.java:439)
E AndroidRuntime: at im.vector.riotx.features.media.RoomEventsAttachmentProvider.overlayViewAtPosition(RoomEventsAttachmentProvider.kt:2)
E AndroidRuntime: at im.vector.riotx.attachmentviewer.AttachmentViewerActivity.onSelectedPositionChanged(AttachmentViewerActivity.kt:15)
E AndroidRuntime: at im.vector.riotx.features.media.VectorAttachmentViewerActivity$onCreate$3.run(VectorAttachmentViewerActivity.kt:1)
E AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:873)
E AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:99)
E AndroidRuntime: at android.os.Looper.loop(Looper.java:193)
E AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:6718)
E AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
E AndroidRuntime: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:491)
E AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
W ActivityManager: Force finishing activity im.vector.app/im.vector.riotx.features.media.VectorAttachmentViewerActivity
W ActivityManager: Force finishing activity im.vector.app/im.vector.riotx.features.home.room.detail.RoomDetailActivity
I ActivityManager: Showing crash dialog for package im.vector.app u0
```