MDEV-34930: MDEV-32014 Galera and SST/no binlog fixes

 1. Binlog commit by rotate (MDEV-32014) should not be
    used with Galera, yet while WSREP binlog emulation
    is active, the code path could lead into
    binlog_cache_data::write_prepare() in an invalid
    state, leading to errors in MTR. To fix, an extra
    check is added to ensure the binlog is actually
    active before calling write_prepare().

 2. If the #binlog_cache_files directory exists on a
    mariadbd run without opt_log_bin, the directory
    was treated as a table/database, leading to errors.
    To fix, on startup, if opt_log_bin is disabled and
    #binlog_cache_files exists (in the default log
    directory), the directory is deleted (and an
    informational message is provided in the error
    log)

Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>

sql/log_cache.cc

@@ -59,9 +59,14 @@ bool init_binlog_cache_dir()
   uint max_tmp_file_name_len=
       2 /* prefix */ + 10 /* max len of thread_id */ + 1 /* underline */;
 
-  ignore_db_dirs_append(BINLOG_CACHE_DIR);
-
-  dirname_part(binlog_cache_dir, log_bin_basename, &length);
+  /*
+    Even if the binary log is disabled (and thereby we wouldn't use the binlog
+    cache), we need to try to build the directory name, so if it exists while
+    the binlog is off (e.g. due to a previous run of mariadbd, or an SST), we
+    can delete it.
+  */
+  dirname_part(binlog_cache_dir,
+               opt_bin_log ? log_bin_basename : opt_log_basename, &length);
   /*
     Must ensure the full name of the tmp file is shorter than FN_REFLEN, to
     avoid overflowing the name buffer in write and commit.
@@ -79,6 +84,27 @@ bool init_binlog_cache_dir()
 
   MY_DIR *dir_info= my_dir(binlog_cache_dir, MYF(0));
 
+  /*
+    If the binlog cache dir exists, yet binlogging is disabled, delete the
+    directory and skip the initialization logic.
+  */
+  if (!opt_bin_log)
+  {
+    if (dir_info)
+    {
+      sql_print_information(
+          "Found binlog cache dir '%s', yet binary logging is "
+          "disabled. Deleting directory.",
+          binlog_cache_dir);
+      my_dirend(dir_info);
+      my_rmtree(binlog_cache_dir, MYF(0));
+    }
+    memset(binlog_cache_dir, 0, sizeof(binlog_cache_dir));
+    return false;
+  }
+
+  ignore_db_dirs_append(BINLOG_CACHE_DIR);
+
   if (!dir_info)
   {
     /* Make a dir for binlog cache temp files if not exist. */

sql/log_event_server.cc

@@ -691,7 +691,11 @@ void Log_event::init_show_field_list(THD *thd, List<Item>* field_list)
 int Log_event_writer::write_internal(const uchar *pos, size_t len)
 {
   DBUG_ASSERT(!ctx || encrypt_or_write == &Log_event_writer::encrypt_and_write);
-  if (cache_data && cache_data->write_prepare(len))
+  if (cache_data &&
+#ifdef WITH_WSREP
+      mysql_bin_log.is_open() &&
+#endif
+      cache_data->write_prepare(len))
     return 1;
 
   if (my_b_safe_write(file, pos, len))

sql/mysqld.cc

@@ -5614,10 +5614,11 @@ static int init_server_components()
     mysql_mutex_unlock(log_lock);
     if (unlikely(error))
       unireg_abort(1);
-    if (unlikely(init_binlog_cache_dir()))
-      unireg_abort(1);
   }
 
+  if (unlikely(init_binlog_cache_dir()))
+    unireg_abort(1);
+
 #ifdef HAVE_REPLICATION
   binlog_space_limit= internal_binlog_space_limit;
   slave_connections_needed_for_purge=