minor update to reduce database read on ui thread

Session/Conversations/ConversationVC.swift

@@ -291,6 +291,7 @@ final class ConversationVC : BaseVC, ConversationViewModelDelegate, OWSConversat
         let viewItem = viewItems[indexPath.row]
         let cell = tableView.dequeueReusableCell(withIdentifier: MessageCell.getCellType(for: viewItem).identifier) as! MessageCell
         cell.delegate = self
+        cell.thread = thread
         cell.viewItem = viewItem
         return cell
     }

Session/Conversations/Message Cells/MessageCell.swift

@@ -1,4 +1,5 @@
 import UIKit
+import SessionMessagingKit
 
 public enum SwipeState {
     case began
@@ -8,7 +9,16 @@ public enum SwipeState {
 
 class MessageCell : UITableViewCell {
     weak var delegate: MessageCellDelegate?
-    var viewItem: ConversationViewItem? { didSet { update() } }
+    var thread: TSThread? {
+        didSet {
+            if viewItem != nil { update() }
+        }
+    }
+    var viewItem: ConversationViewItem? {
+        didSet {
+            if thread != nil { update() }
+        }
+    }
     
     // MARK: Settings
     class var identifier: String { preconditionFailure("Must be overridden by subclasses.") }

Session/Conversations/Message Cells/VisibleMessageCell.swift

@@ -257,7 +257,7 @@ final class VisibleMessageCell : MessageCell, LinkPreviewViewDelegate {
         messageStatusImageView.image = image
         messageStatusImageView.backgroundColor = backgroundColor
         if let message = message as? TSOutgoingMessage {
-            messageStatusImageView.isHidden = (message.messageState == .sent && message.thread.lastInteraction != message)
+            messageStatusImageView.isHidden = (message.messageState == .sent && thread?.lastInteraction != message)
         } else {
             messageStatusImageView.isHidden = true
         }
@@ -349,7 +349,7 @@ final class VisibleMessageCell : MessageCell, LinkPreviewViewDelegate {
             }
         case .mediaMessage:
             if viewItem.interaction is TSIncomingMessage,
-                let thread = viewItem.interaction.thread as? TSContactThread,
+                let thread = thread as? TSContactThread,
                 Storage.shared.getContact(with: thread.contactSessionID())?.isTrusted != true {
                 showMediaPlaceholder()
             } else {
@@ -382,7 +382,7 @@ final class VisibleMessageCell : MessageCell, LinkPreviewViewDelegate {
             }
         case .audio:
             if viewItem.interaction is TSIncomingMessage,
-                let thread = viewItem.interaction.thread as? TSContactThread,
+                let thread = thread as? TSContactThread,
                 Storage.shared.getContact(with: thread.contactSessionID())?.isTrusted != true {
                 showMediaPlaceholder()
             } else {
@@ -393,7 +393,7 @@ final class VisibleMessageCell : MessageCell, LinkPreviewViewDelegate {
             }
         case .genericAttachment:
             if viewItem.interaction is TSIncomingMessage,
-                let thread = viewItem.interaction.thread as? TSContactThread,
+                let thread = thread as? TSContactThread,
                 Storage.shared.getContact(with: thread.contactSessionID())?.isTrusted != true {
                 showMediaPlaceholder()
             } else {
@@ -673,7 +673,7 @@ final class VisibleMessageCell : MessageCell, LinkPreviewViewDelegate {
 
     private static func shouldShowProfilePicture(for viewItem: ConversationViewItem) -> Bool {
         guard let message = viewItem.interaction as? TSMessage else { preconditionFailure() }
-        let isGroupThread = message.thread.isGroupThread()
+        let isGroupThread = viewItem.isGroupThread
         let senderSessionID = (message as? TSIncomingMessage)?.authorId
         return isGroupThread && viewItem.shouldShowSenderProfilePicture && senderSessionID != nil
     }