Refactor the channel::self to point at the existing user

This way, the user is always up to date, instead of being a duplicate out of
sync.

fix #3258

src/irc/irc_channel.cpp

@@ -1,21 +1,25 @@
 #include <irc/irc_channel.hpp>
 #include <algorithm>
 
-void IrcChannel::set_self(const std::string& name)
+void IrcChannel::set_self(IrcUser* user)
 {
-  this->self = std::make_unique<IrcUser>(name);
+  this->self = user;
 }
 
 IrcUser* IrcChannel::add_user(const std::string& name,
                               const std::map<char, char>& prefix_to_mode)
 {
-  this->users.emplace_back(std::make_unique<IrcUser>(name, prefix_to_mode));
+  auto new_user = std::make_unique<IrcUser>(name, prefix_to_mode);
+  auto old_user = this->find_user(new_user->nick);
+  if (old_user)
+    return old_user;
+  this->users.emplace_back(std::move(new_user));
   return this->users.back().get();
 }
 
 IrcUser* IrcChannel::get_self() const
 {
-  return this->self.get();
+  return this->self;
 }
 
 IrcUser* IrcChannel::find_user(const std::string& name) const
@@ -32,19 +36,27 @@ IrcUser* IrcChannel::find_user(const std::string& name) const
 void IrcChannel::remove_user(const IrcUser* user)
 {
   const auto nick = user->nick;
+  const bool is_self = (user == this->self);
   const auto it = std::find_if(this->users.begin(), this->users.end(),
                                [nick](const std::unique_ptr<IrcUser>& u)
                                {
                                  return nick == u->nick;
                                });
   if (it != this->users.end())
-    this->users.erase(it);
+    {
+      this->users.erase(it);
+      if (is_self)
+        {
+          this->self = nullptr;
+          this->joined = false;
+        }
+    }
 }
 
 void IrcChannel::remove_all_users()
 {
   this->users.clear();
-  this->self.reset();
+  this->self = nullptr;
 }
 
 DummyIrcChannel::DummyIrcChannel():