MDEV-37553: Assertion failure lsn - get_flushed_lsn(...) < capacity()

log_t::append_prepare_wait(): Relax the debug assertion in case
log_overwrite_warning() has been called. In this case, the
contents of log_sys.buf (and the ib_logfile0) is basically
unrecoverable garbage, and it does not matter which write was
last persisted.

This assertion would easily fail in the 11.4 branch in the test
encryption.innochecksum after merging MDEV-36024.

Author: dr-m

storage/innobase/mtr/mtr0mtr.cc

@@ -909,7 +909,8 @@ ATTRIBUTE_COLD void log_t::append_prepare_wait(bool late, bool ex) noexcept
     const bool is_pmem{is_mmap()};
     if (is_pmem)
     {
-      ut_ad(lsn - get_flushed_lsn(std::memory_order_relaxed) < capacity());
+      ut_ad(lsn - get_flushed_lsn(std::memory_order_relaxed) < capacity() ||
+            overwrite_warned);
       persist(lsn);
     }
 #endif