Fix race in shutdown thread start (#8380)

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.

Co-authored-by: Artyom Ivanov <[email protected]>

Author: TreeHunter9

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()