input/Tidal*Request: add Start() method

The caller should be able to safely store the instance pointer before
his callback is invoked.

src/input/plugins/TidalInputPlugin.cxx

@@ -91,6 +91,7 @@ TidalInputStream::OnTidalSession() noexcept
 								    tidal_session->GetSession().c_str(),
 								    track_id.c_str(),
 								    handler);
+		track_request->Start();
 	} catch (...) {
 		Failed(std::current_exception());
 	}

src/input/plugins/TidalLoginRequest.cxx

@@ -59,8 +59,6 @@ TidalLoginRequest::TidalLoginRequest(CurlGlobal &curl,
 	request.SetOption(CURLOPT_COPYPOSTFIELDS,
 			  EncodeForm(request.Get(),
 				     {{"username", username}, {"password", password}}).c_str());
-
-	request.StartIndirect();
 }
 
 TidalLoginRequest::~TidalLoginRequest() noexcept

src/input/plugins/TidalLoginRequest.hxx

@@ -44,6 +44,8 @@ public:
 
 /**
  * An asynchronous Tidal "login/username" request.
+ *
+ * After construction, call Start() to initiate the request.
  */
 class TidalLoginRequest final : CurlResponseHandler {
 	CurlSlist request_headers;
@@ -71,6 +73,10 @@ public:
 
 	~TidalLoginRequest() noexcept;
 
+	void Start() {
+		request.StartIndirect();
+	}
+
 private:
 	/* virtual methods from CurlResponseHandler */
 	void OnHeaders(unsigned status,

src/input/plugins/TidalSessionManager.cxx

@@ -60,6 +60,7 @@ TidalSessionManager::AddLoginHandler(TidalSessionHandler &h) noexcept
 								    token,
 								    username, password,
 								    handler);
+			login_request->Start();
 		} catch (...) {
 			error = std::current_exception();
 			ScheduleInvokeHandlers();

src/input/plugins/TidalTrackRequest.cxx

@@ -61,8 +61,6 @@ TidalTrackRequest::TidalTrackRequest(CurlGlobal &curl,
 	request_headers.Append((std::string("X-Tidal-SessionId:")
 				+ session).c_str());
 	request.SetOption(CURLOPT_HTTPHEADER, request_headers.Get());
-
-	request.StartIndirect();
 }
 
 TidalTrackRequest::~TidalTrackRequest() noexcept

src/input/plugins/TidalTrackRequest.hxx

@@ -46,6 +46,8 @@ public:
 
 /**
  * An asynchronous request for the streaming URL of a Tidal track.
+ *
+ * After construction, call Start() to initiate the request.
  */
 class TidalTrackRequest final : CurlResponseHandler {
 	CurlSlist request_headers;
@@ -74,6 +76,10 @@ public:
 
 	~TidalTrackRequest() noexcept;
 
+	void Start() {
+		request.StartIndirect();
+	}
+
 private:
 	/* virtual methods from CurlResponseHandler */
 	void OnHeaders(unsigned status,