fix: replace alpha update with isVisible to not intercept tap from message gestures (#809)

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/ConversationActivityV2.kt

@@ -714,7 +714,6 @@ class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDe
     }
 
     private fun handleRecyclerViewScrolled() {
-        val alpha = if (!isScrolledToBottom) 1.0f else 0.0f
         // FIXME: Checking isScrolledToBottom is a quick fix for an issue where the
         //        typing indicator overlays the recycler view when scrolled up
         val wasTypingIndicatorVisibleBefore = typingIndicatorViewContainer.isVisible
@@ -723,7 +722,7 @@ class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDe
         if (isTypingIndicatorVisibleAfter != wasTypingIndicatorVisibleBefore) {
             inputBarHeightChanged(inputBar.height)
         }
-        scrollToBottomButton.alpha = alpha
+        scrollToBottomButton.isVisible = !isScrolledToBottom
         unreadCount = min(unreadCount, layoutManager.findFirstVisibleItemPosition())
         updateUnreadCountIndicator()
     }

app/src/main/res/layout/activity_conversation_v2.xml

@@ -94,8 +94,7 @@
         android:layout_alignParentRight="true"
         android:layout_alignParentBottom="true"
         android:layout_marginRight="12dp"
-        android:layout_marginBottom="72dp"
-        android:alpha="1">
+        android:layout_marginBottom="72dp">
 
         <RelativeLayout
             android:layout_width="40dp"