MDEV-29593 fixup: Avoid a leak if rseg.undo_cached is corrupted

trx_purge_truncate_rseg_history(): Avoid a leak similar to the one
that was fixed in MDEV-31324, in case a supposedly cached undo log
page is not found in the rseg.undo_cached list.

Author: dr-m

storage/innobase/trx/trx0purge.cc

@@ -510,9 +510,9 @@ trx_purge_truncate_rseg_history(trx_rseg_t& rseg,
         if (undo->hdr_page_no == hdr_addr.page)
           goto found_cached;
       ut_ad("inconsistent undo logs" == 0);
-      break;
-    found_cached:
-      UT_LIST_REMOVE(rseg.undo_cached, undo);
+      if (false)
+      found_cached:
+        UT_LIST_REMOVE(rseg.undo_cached, undo);
       static_assert(FIL_NULL == 0xffffffff, "");
       if (UNIV_UNLIKELY(mach_read_from_4(TRX_RSEG + TRX_RSEG_FORMAT +
                                          rseg_hdr->page.frame)))