LibTLS: Use a setter for on_tls_ready_to_write with some more smarts

The callback should be called as soon as the connection is established,
and if we actually set the callback when it already is, we expect it to
be called immediately.

Userland/Libraries/LibHTTP/HttpsJob.cpp

@@ -68,6 +68,7 @@ void HttpsJob::shutdown()
         return;
     m_socket->on_tls_ready_to_read = nullptr;
     m_socket->on_tls_connected = nullptr;
+    m_socket->set_on_tls_ready_to_write(nullptr);
     m_socket = nullptr;
 }
 
@@ -97,9 +98,10 @@ void HttpsJob::register_on_ready_to_read(Function<void()> callback)
 
 void HttpsJob::register_on_ready_to_write(Function<void()> callback)
 {
-    m_socket->on_tls_ready_to_write = [callback = move(callback)](auto&) {
+    m_socket->set_on_tls_ready_to_write([callback = move(callback)](auto& tls) {
+        Core::deferred_invoke([&tls] { tls.set_on_tls_ready_to_write(nullptr); });
         callback();
-    };
+    });
 }
 
 bool HttpsJob::can_read_line() const