Fix race in shutdown thread start

Previously we assign value to shutdownSemaphore after shutdownThread is started, where it is already needed. So we can have situation where shutdownThread instantly leaving due to shutdownSemaphore == nullptr, and we are left with a server that can only be stopped with kill -9.

Author: Artyom Ivanov

src/yvalve/why.cpp

@@ -831,11 +831,11 @@ class ShutdownInit
 		explicit CtrlCHandler(MemoryPool& p)
 			: ShutdownInit(p)
 		{
+			shutdownSemaphore = &semaphore;
 			Thread::start(shutdownThread, 0, 0, &handle);
 
 			procInt = ISC_signal(SIGINT, handlerInt, 0);
 			procTerm = ISC_signal(SIGTERM, handlerTerm, 0);
-			shutdownSemaphore = &semaphore;
 		}
 
 		~CtrlCHandler()