Fixed a chatlog problem with new mariadb versions

Fixes #5661

Thanks to @mazvi

src/map/log.cpp

@@ -466,6 +466,10 @@ void log_chat(e_log_chat_type type, int type_id, int src_charid, int src_accid,
 		return;
 	}
 
+	if( dst_charname == nullptr ){
+		dst_charname = "";
+	}
+
 	if( log_config.sql_logs ) {
 		SqlStmt* stmt;