Move the handle idle command into the command queue

My theory is that it's ok to send the `noidle` synchronously but the
subsequent handling of the idle response should be on the command queue.
My hope is that this fixes issues with less than perfect network
connections (and also very occasionally seen on good networks).

Shared/MPDClient/Extensions/MPDClient+Command.swift

@@ -158,7 +158,7 @@ extension MPDClient {
 
     let commandOperation = BlockOperation() { [unowned self] in
       self.sendCommand(command: command, userData: userData)
-
+  
       if self.checkError() {
         self.idle(forceIdle)
       }

Shared/MPDClient/Extensions/MPDClient+Idle.swift

@@ -12,50 +12,37 @@ import mpdclient
 extension MPDClient {
   func noIdle() {
     guard isConnected else { return }
-
-    do {
-      idleLock.lock()
-      defer { idleLock.unlock() }
-      if isIdle {
-        mpd_send_noidle(connection)
-        isIdle = false
-      }
+    
+    if isIdle {
+      mpd_send_noidle(connection)
     }
   }
 
   func idle(_ force: Bool = false) {
     guard isConnected else { return }
 
-    let shouldIdle: Bool
-  
-    do {
-      idleLock.lock()
-      defer { idleLock.unlock() }
-      shouldIdle = (!isIdle && commandQueue.operationCount == 1) || force
-      if shouldIdle {
-        mpd_send_idle(connection)
-        self.isIdle = true
-      }
-    }
-
+    let shouldIdle: Bool = (!isIdle && commandQueue.operationCount == 1) || force
+    
     if shouldIdle {
-      let result = mpd_recv_idle(connection, true)
-      handleIdleResult(result)
+      self.isIdle = true
+      mpd_send_idle(connection)
+      
+      let handleIdleOperation = BlockOperation() { [unowned self] in
+        self.handleIdleResult()
+      }
+      
+      handleIdleOperation.queuePriority = .high
+      commandQueue.addOperation(handleIdleOperation)
     }
   }
 
-  func handleIdleResult(_ result: mpd_idle) {
+  func handleIdleResult() {
+    let result = mpd_recv_idle(connection, true)
     let mpdIdle = MPDIdle(rawValue: result.rawValue)
-    let wasIdle: Bool
+    
+    isIdle = false
 
-    do {
-      idleLock.lock()
-      defer { idleLock.unlock() }
-      wasIdle = isIdle
-      isIdle = false
-    }
-  
-    if checkError() && wasIdle {
+    if checkError() {
       if mpdIdle.contains(.database) {
         self.fetchAllAlbums()
       }

Shared/MPDClient/MPDClient.swift

@@ -21,8 +21,6 @@ class MPDClient {
   var queue: [MPDSong] = []
 
   let commandQueue = OperationQueue()
-  
-  let idleLock = NSLock()
 
   init(withDelegate delegate: MPDClientDelegate?) {
     commandQueue.maxConcurrentOperationCount = 1