Fix compilation with compilers not supporting auto(x)

Author: mawww

src/client_manager.cc

@@ -77,7 +77,7 @@ Client* ClientManager::create_client(std::unique_ptr<UserInterface>&& ui, int pi
         context.window().center_line(init_coord->line);
     }
 
-    auto(std::move(unlock)); // unlock now
+    unlock.trigger();
 
     try
     {

src/utils.hh

@@ -72,6 +72,9 @@ public:
       : m_valid{other.m_valid}, m_func{std::move(other.m_func)}
     { other.m_valid = false; }
 
+    [[gnu::always_inline]]
+    void trigger() { if (m_valid) m_func(); m_valid = false; }
+
     [[gnu::always_inline]]
     ~OnScopeEnd() noexcept(noexcept(m_func())) { if (m_valid) m_func(); }