MDEV-28429 audit plugin report OOOOO.

Few initializations to the connection_info structure added.
I think they can be removed if we are sure the bug was fixed.

plugin/server_audit/server_audit.c

@@ -15,7 +15,7 @@
 
 
 #define PLUGIN_VERSION 0x104
-#define PLUGIN_STR_VERSION "1.4.13"
+#define PLUGIN_STR_VERSION "1.4.14"
 
 #define _my_thread_var loc_thread_var
 
@@ -945,7 +945,19 @@ static unsigned long long query_counter= 1;
 
 static struct connection_info *get_loc_info(MYSQL_THD thd)
 {
+  /*
+    This is the original code and supposed to be returned
+    bach to this as the MENT-1438 is finally understood/resolved.
   return (struct connection_info *) THDVAR(thd, loc_info);
+  */
+  struct connection_info *ci= (struct connection_info *) THDVAR(thd, loc_info);
+  if ((size_t) ci->user_length > sizeof(ci->user))
+  {
+    ci->user_length= 0;
+    ci->host_length= 0;
+    ci->ip_length= 0;
+  }
+  return ci;
 }
 
 
@@ -1373,6 +1385,16 @@ static size_t log_header(char *message, size_t message_len,
     host= userip;
   }
 
+  /*
+    That was added to find the possible cause of the MENT-1438.
+    Supposed to be removed after that.
+  */
+  if (username_len > 1024)
+  {
+    username= "unknown_user";
+    username_len= (unsigned int) strlen(username);
+  }
+
   if (output_type == OUTPUT_SYSLOG)
     return my_snprintf(message, message_len,
         "%.*s,%.*s,%.*s,%d,%lld,%s",