fix an issue where untrusted contact's media message will never be marked as read

SessionMessagingKit/Messages/Signal/TSIncomingMessage.m

@@ -155,8 +155,15 @@ NS_ASSUME_NONNULL_BEGIN
     if (_read && readTimestamp >= self.expireStartedAt) {
         return;
     }
+    BOOL isTrusted = YES;
+    TSThread* thread = [self threadWithTransaction:transaction];
+    if ([thread isKindOfClass:[TSContactThread class]]) {
+        TSContactThread* contactThread = (TSContactThread*)thread;
+        isTrusted = [[LKStorage shared] getContactWithSessionID:[contactThread contactSessionID] using:transaction].isTrusted;
+    }
     
     BOOL areAllAttachmentsDownloaded = YES;
+    if (isTrusted) {
         for (NSString *attachmentId in self.attachmentIds) {
             TSAttachment *attachment = [TSAttachment fetchObjectWithUniqueID:attachmentId transaction:transaction];
             // If the attachment download failed, we can mark this message as read.
@@ -168,6 +175,7 @@ NS_ASSUME_NONNULL_BEGIN
             areAllAttachmentsDownloaded = areAllAttachmentsDownloaded && attachment.isDownloaded;
             if (!areAllAttachmentsDownloaded) break;
         }
+    }
     
     if (!areAllAttachmentsDownloaded) {
         return;