Fix uninitialized max_allowed_pkt in MySQL_Connection constructor

Initialize options.max_allowed_pkt to 0 to prevent Valgrind errors
when logging handshake debug information.

lib/mysql_connection.cpp

@@ -457,6 +457,7 @@ MySQL_Connection::MySQL_Connection() {
 	options.ldap_user_variable_sent=false;
 	options.session_track_gtids_int=0;
 	options.server_capabilities=0;
+	options.max_allowed_pkt=0;
 
 	compression_pkt_id=0;
 	mysql_result=NULL;