Fix crash when setting up key backup

You must supply a layout_height/width attribute

vector/src/main/res/layout/fragment_keys_backup_setup_step1.xml

@@ -84,6 +84,8 @@
     <Button
         android:id="@+id/keys_backup_setup_step1_manual_export_button"
         style="@style/Widget.Vector.Button.Text"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
         android:layout_margin="16dp"
         android:layout_marginStart="@dimen/layout_horizontal_margin"
         android:layout_marginEnd="@dimen/layout_horizontal_margin"