Don't start app version migrations until storage is ready.

SignalMessaging/environment/AppSetup.m

@@ -52,6 +52,7 @@ NS_ASSUME_NONNULL_BEGIN
         [NSKeyedUnarchiver setClass:[OWSDatabaseMigration class] forClassName:[OWSDatabaseMigration collection]];
 
         [OWSStorage setupStorageWithMigrationBlock:^() {
+            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                 // Don't start database migrations until storage is ready.
                 [VersionMigrations performUpdateCheckWithCompletion:^() {
                     OWSAssertIsOnMainThread();
@@ -60,6 +61,7 @@ NS_ASSUME_NONNULL_BEGIN
 
                     backgroundTask = nil;
                 }];
+            });
         }];
         [[Environment current].contactsManager startObserving];
     });