Prevent conversion to client on suspend from disconnecting other clients

clear the client manager in the to be converted process without
sending exit messages as the forked server will still be there.

Fixes #2847

src/buffer_manager.cc

@@ -21,7 +21,7 @@ BufferManager::~BufferManager()
 
     // Make sure not clients exists
     if (ClientManager::has_instance())
-        ClientManager::instance().clear();
+        ClientManager::instance().clear(true);
 }
 
 Buffer* BufferManager::create_buffer(String name, Buffer::Flags flags,

src/client_manager.cc

@@ -14,13 +14,18 @@ namespace Kakoune
 ClientManager::ClientManager() = default;
 ClientManager::~ClientManager()
 {
-    clear();
+    clear(true);
 }
 
-void ClientManager::clear()
+void ClientManager::clear(bool disconnect_clients)
 {
+    if (disconnect_clients)
+    {
         while (not m_clients.empty())
             remove_client(*m_clients.front(), true, 0);
+    }
+    else
+        m_clients.clear();
     m_client_trash.clear();
 
     for (auto& window : m_free_windows)

src/client_manager.hh

@@ -27,7 +27,7 @@ public:
     bool   empty() const { return m_clients.empty(); }
     size_t count() const { return m_clients.size(); }
 
-    void clear();
+    void clear(bool exit);
 
     void ensure_no_client_uses_buffer(Buffer& buffer);
 

src/main.cc

@@ -801,6 +801,7 @@ int run_server(StringView session, StringView server_init,
 
                 if (fork_server_to_background())
                 {
+                    ClientManager::instance().clear(false);
                     String session = server.session();
                     server.close_session(false);
                     throw convert_to_client_mode{ std::move(session), std::move(client_name), std::move(buffer_name), std::move(selections) };