Can only set whitelist on main thread

As written solves a crash, but we'll probalby want to revisit the perf
implications.

// FREEBIE

SignalServiceKit/src/Protocols/ProtoBuf+OWS.m

@@ -55,7 +55,10 @@ 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];
+            });
         }
     }
 }