fix issue with avatar background recycling (#1209)

app/src/main/java/com/keylesspalace/tusky/adapter/StatusBaseViewHolder.java

@@ -193,6 +193,7 @@ public abstract class StatusBaseViewHolder extends RecyclerView.ViewHolder {
             avatarInset.setImageResource(R.drawable.ic_bot_24dp);
             avatarInset.setBackgroundColor(0x50ffffff);
         } else {
+            avatarInset.setBackground(null);
             avatarInset.setVisibility(View.GONE);
         }
     }