Bug#43733 Select on processlist let the embedded server crash (concurrent_innodb_safelog)

the thread->mysys_var parameter should be empty for the idle
    embedded-server threads so that working threads can safely free
    this memory.

per-file comments:
  libmysqld/lib_sql.cc
Bug#43733      Select on processlist let the embedded server crash (concurrent_innodb_safelog)
    set thread->mysys_var= 0 after the query is handled

  mysql-test/include/concurrent.inc
Bug#43733      Select on processlist let the embedded server crash (concurrent_innodb_safelog)
    enable these for the embedded-server mode

  sql/sql_show.cc
Bug#43733      Select on processlist let the embedded server crash (concurrent_innodb_safelog)
    show thread lock status in the query result

libmysqld/lib_sql.cc

@@ -142,6 +142,8 @@ emb_advanced_command(MYSQL *mysql, enum enum_server_command command,
   if (!skip_check)
     result= thd->is_error() ? -1 : 0;
 
+  thd->mysys_var= 0;
+
 #if defined(ENABLED_PROFILING) && defined(COMMUNITY_SERVER)
   thd->profiling.finish_current_query();
 #endif
@@ -634,6 +636,7 @@ void *create_embedded_thd(int client_flag)
 
   thread_count++;
   threads.append(thd);
+  thd->mysys_var= 0;
   return thd;
 err:
   delete(thd);

mysql-test/include/concurrent.inc

@@ -25,8 +25,6 @@
 #               new wrapper t/concurrent_innodb_safelog.test
 #
 
---source include/not_embedded.inc
-
 connection default;
 #
 # Show prerequisites for this test.

sql/sql_show.cc

@@ -1888,7 +1888,7 @@ int fill_schema_processlist(THD* thd, TABLE_LIST* tables, COND* cond)
                     tmp->mysys_var->current_cond ?
                     "Waiting on cond" : NullS);
 #else
-      val= (char *) "Writing to net";
+      val= (char *) (tmp->proc_info ? tmp->proc_info : NullS);
 #endif
       if (val)
       {