adapter check background tint

Change-Id: I4cd4f49772a203765745626fdf17b0c4b7126e49

jami-android/app/src/main/java/cx/ring/adapters/ConversationAdapter.kt

@@ -849,7 +849,7 @@ class ConversationAdapter(
                 val isDeleted = textMessage.body.isNullOrEmpty()
                 val msgTxt = convViewHolder.mMsgTxt ?: return@subscribe
                 val longPressView = convViewHolder.mMsgTxt!!
-                longPressView.background.setTintList(null)
+                longPressView.background?.setTintList(null)
                 val isTimeShown = hasPermanentTimeString(textMessage, position)
                 val msgSequenceType = getMsgSequencing(position, isTimeShown)
                 if (isDeleted) {