update lwmqtt_client_t initialization

[amarkevich]

to avoid

In file included from [cut]\Arduino\libraries\MQTT\src\MQTTClient.cpp:1:0:
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::keep_alive_interval' [-Wmissing-field-initializers]
lwmqtt_client_t client = {0};
^
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::pong_pending' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::write_buf_size' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::read_buf_size' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::write_buf' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::read_buf' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::callback' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::callback_ref' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::network' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::network_read' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::network_write' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::keep_alive_timer' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::command_timer' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::timer_set' [-Wmissing-field-initializers]
Arduino\libraries\MQTT\src\MQTTClient.h:53:30: warning: missing initializer for member 'lwmqtt_client_t::timer_get' [-Wmissing-field-initializers]

[256dpi]

Thanks!