MDEV-31442 page_cleaner thread aborts while releasing the tablespace

After further I/O on a tablespace has been stopped
(for example due to DROP TABLE or an operation that
rebuilds a table), page cleaner thread tries to
flush the pending writes for the tablespace and
releases the tablespace reference even though it was not
acquired.

fil_space_t::flush(): Don't release the tablespace when it is
being stopped and closed

Thanks to Marko Mäkelä for suggesting this patch.

storage/innobase/include/fil0fil.h

@@ -1526,9 +1526,11 @@ template<bool have_reference> inline void fil_space_t::flush()
     flush_low();
   else
   {
-    if (!(acquire_low() & (STOPPING | CLOSING)))
+    if (!(acquire_low(STOPPING & CLOSING) & (STOPPING | CLOSING)))
+    {
       flush_low();
-    release();
+      release();
+    }
   }
 }