Fix wrong statement when clearing active channels

Author: zlmr

templates/swift/Sources/Services/Realtime.swift.twig

@@ -137,7 +137,7 @@ open class Realtime : Service {
             let subsWithChannel = activeSubscriptions.filter { callback in
                 return callback.value.channels.contains(channel)
             }
-            return subsWithChannel.isEmpty
+            return !subsWithChannel.isEmpty
         }
     }
 }