shared/daemon-util: fix notify_on_cleanup()

p itself is never null. Because of this, we would always
call sd_notify() in cleanup, even though the intention was to only
call it if notify_start() was executed.

src/shared/daemon-util.h

@@ -17,6 +17,6 @@ static inline const char *notify_start(const char *start, const char *stop) {
 
 /* This is intended to be used with _cleanup_ attribute. */
 static inline void notify_on_cleanup(const char **p) {
-        if (p)
+        if (*p)
                 (void) sd_notify(false, *p);
 }