White listing must happen on main thread

followup to: ee613e4889

Again, this solves a crash, but we'll want to revisit the perf
implications.

// FREEBIE

SignalServiceKit/src/Protocols/ProtoBuf+OWS.m

@@ -80,7 +80,10 @@ NS_ASSUME_NONNULL_BEGIN
         // Once we've shared our profile key with a user (perhaps due to being
         // a member of a whitelisted group), make sure they're whitelisted.
         id<ProfileManagerProtocol> profileManager = [TextSecureKitEnv sharedEnv].profileManager;
-        [profileManager addUserToProfileWhitelist:recipientId];
+        // FIXME PERF avoid this dispatch. It's going to happen for *each* recipient in a group message.
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [profileManager addUserToProfileWhitelist:recipientId];
+        });
     }
 }