tree-wide: avoid uninitialized warning on _cleanup_ variables

With some versions of the compiler, the _cleanup_ attr makes it think
the variable might be freed/closed when uninitialized, even though it
cannot happen. The added cost is small enough to be worth the benefit,
and optimized builds will help reduce it even further.

src/timesync/wait-sync.c

@@ -179,7 +179,7 @@ static int clock_state_update(
 }
 
 static int run(int argc, char * argv[]) {
-        _cleanup_(sd_event_unrefp) sd_event *event;
+        _cleanup_(sd_event_unrefp) sd_event *event = NULL;
         _cleanup_(clock_state_release) ClockState state = {
                 .timerfd_fd = -1,
                 .inotify_fd = -1,