quartz/systemclock: Avoid a use-after-free (Coverity).

Signed-off-by: Zebediah Figura <z.figura12@gmail.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/quartz/systemclock.c

@@ -85,6 +85,7 @@ static DWORD WINAPI SystemClockAdviseThread(void *param)
                     SetEvent(sink->handle);
                     list_remove(&sink->entry);
                     heap_free(sink);
+                    continue;
                 }
             }