event/Loop: destruct the Uring::Manager in the destructor before assert()

Fixes assertion failure when the EventLoop gets destructed before
Run() was ever called.

Fixes https://bugs.debian.org/998310

NEWS

@@ -1,4 +1,5 @@
 ver 0.23.4 (not yet released)
+* fix crash or debug builds if startup fails
 
 ver 0.23.3 (2021/10/31)
 * protocol

src/event/Loop.cxx

@@ -52,6 +52,13 @@ EventLoop::EventLoop(
 
 EventLoop::~EventLoop() noexcept
 {
+#if defined(HAVE_URING) && !defined(NDEBUG)
+	/* if Run() was never called (maybe because startup failed and
+	   an exception is pending), we need to destruct the
+	   Uring::Manager here or else the assertions below fail */
+	uring.reset();
+#endif
+
 	assert(defer.empty());
 	assert(idle.empty());
 #ifdef HAVE_THREADED_EVENT_LOOP