MDEV-27787 mariadb-backup --backup is allocating extra memory for log records

In commit 685d958e (MDEV-14425),
the log parsing in mariadb-backup --backup was rewritten.
The parameter STORE_IF_EXISTS that is being passed to recv_sys.parse_mtr()
or recv_sys.parse_pmem() instead of STORE_NO caused unnecessary additional
memory allocation for redo log records.

extra/mariabackup/xtrabackup.cc

@@ -3003,7 +3003,7 @@ static bool xtrabackup_copy_logfile()
 #ifdef HAVE_PMEM
     if (log_sys.is_pmem())
     {
-      if ((ut_d(r=) recv_sys.parse_pmem(STORE_IF_EXISTS)) != recv_sys_t::OK)
+      if ((ut_d(r=) recv_sys.parse_pmem(STORE_NO)) != recv_sys_t::OK)
       {
         ut_ad(r == recv_sys_t::GOT_EOF);
         goto retry;
@@ -3073,7 +3073,7 @@ static bool xtrabackup_copy_logfile()
 
         start_offset= recv_sys.offset;
       }
-      while ((ut_d(r=)recv_sys.parse_pmem(STORE_IF_EXISTS)) == recv_sys_t::OK);
+      while ((ut_d(r=)recv_sys.parse_pmem(STORE_NO)) == recv_sys_t::OK);
 
       ut_ad(r == recv_sys_t::GOT_EOF);
       pthread_cond_broadcast(&scanned_lsn_cond);
@@ -3109,7 +3109,7 @@ static bool xtrabackup_copy_logfile()
       if (log_sys.buf[recv_sys.offset] <= 1)
         break;
 
-      if (recv_sys.parse_mtr(STORE_IF_EXISTS) == recv_sys_t::OK)
+      if (recv_sys.parse_mtr(STORE_NO) == recv_sys_t::OK)
       {
         do
         {
@@ -3119,7 +3119,7 @@ static bool xtrabackup_copy_logfile()
                                                  sequence_offset));
           *seq= 1;
         }
-        while ((r= recv_sys.parse_mtr(STORE_IF_EXISTS)) == recv_sys_t::OK);
+        while ((r= recv_sys.parse_mtr(STORE_NO)) == recv_sys_t::OK);
 
         if (ds_write(dst_log_file, log_sys.buf + start_offset,
                      recv_sys.offset - start_offset))