Bug #44115 purge_relay_logs doesn't return an error when count_relay_log_space fails

purge_relay_logs() did not propagate an error happend in count_relay_log_space().

Fixed with the suggestesd setting the error= true.
Note, propagation generally out of purge_relay_logs() was fixed for Bug #44179,
and the issue does not exist in 6.0 thanks to a patch for WL#2775.

sql/rpl_rli.cc

@@ -947,6 +947,7 @@ int purge_relay_logs(Relay_log_info* rli, THD *thd, bool just_reset,
   if (count_relay_log_space(rli))
   {
     *errmsg= "Error counting relay log space";
+    error=1;
     goto err;
   }
   if (!just_reset)