MDEV-4815 - allow multiple mysql_server_init() / mysql_server_end() in the same process, for embedded library.

- Reset  static variables that are used to signal "init done"  for DBUG, in dbug_end()
- Set string server variables to NULL after memory for the value is freed - avoids double free()
- fix DBUG_ASSERTs that happened during reinitialization.

1 files changed, 1 insertions, 0 deletions

diff --git a/dbug/dbug.c b/dbug/dbug.c
index b285b32fa17..db5ecb7b95e 100644
--- a/dbug/dbug.c
+++ b/dbug/dbug.c
@@ -1642,6 +1642,7 @@ void _db_end_()
 
   cs->stack= &init_settings;
   FreeState(cs, 0);
+  init_done= 0;
 }