Fix link preview crash.

Signal/src/Loki/LokiGroupChatPoller.swift

@@ -104,7 +104,7 @@ public final class LokiGroupChatPoller : NSObject {
             }
         }
         // Poll
-        let _ = LokiGroupChatAPI.getMessages(for: group.serverID, on: group.server).done { messages in
+        let _ = LokiGroupChatAPI.getMessages(for: group.serverID, on: group.server).done(on: .main) { messages in
             messages.reversed().forEach { message in
                 if message.hexEncodedPublicKey != userHexEncodedPublicKey {
                     processIncomingMessage(message)

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -1407,6 +1407,7 @@ NS_ASSUME_NONNULL_BEGIN
                     [self.primaryStorage setIDForMessageWithServerID:dataMessage.publicChatInfo.serverID to:incomingMessage.uniqueId in:transaction];
                 }
 
+                dispatch_async(dispatch_get_main_queue(), ^{
                     NSString *url = [OWSLinkPreview previewURLForRawBodyText:incomingMessage.body];
                     if (url != nil) {
                         [OWSLinkPreview tryToBuildPreviewInfoObjcWithPreviewUrl:url]
@@ -1418,6 +1419,7 @@ NS_ASSUME_NONNULL_BEGIN
                             }];
                         });
                     }
+                });
 
                 return incomingMessage;
             }
@@ -1505,6 +1507,7 @@ NS_ASSUME_NONNULL_BEGIN
                           transaction:transaction];
 
         if (linkPreview != nil) {
+            dispatch_async(dispatch_get_main_queue(), ^{
                 [OWSLinkPreview tryToBuildPreviewInfoObjcWithPreviewUrl:linkPreview.urlString]
                 .thenOn(dispatch_get_main_queue(), ^(OWSLinkPreviewDraft *linkPreviewDraft) {
                     if (linkPreviewDraft.jpegImageData == nil) { return; }
@@ -1515,6 +1518,7 @@ NS_ASSUME_NONNULL_BEGIN
                         [incomingMessage saveWithTransaction:transaction];
                     }];
                 });
+            });
         };
         
         return incomingMessage;

SignalServiceKit/src/Messages/OWSMessageSender.m

@@ -1544,7 +1544,7 @@ NSString *const OWSMessageSenderRateLimitedException = @"RateLimitedException";
             
             // A friend request means we don't have a session with the person
             // There's no point to check for it
-            Boolean isFriendRequest = [messageSend.message isKindOfClass:LKFriendRequestMessage.class];
+            BOOL isFriendRequest = [messageSend.message isKindOfClass:LKFriendRequestMessage.class];
             if (!isFriendRequest) {
                 [self throws_ensureRecipientHasSessionForMessageSend:messageSend deviceId:deviceId];
             }