WebUI is missing quotes on placeholder attributes

[g-regor]

For example when MQTT_SERVER is set to "", HTML is served as <input id='mh' placeholder= value='mqtt-broker.local'>, which the browser parses as <input id="mh" placeholder="value='mqtt-broker.local'" name="mh"> and is then shown as

The same problem also occurs for MQTT_PORT, MQTT_USER and Gateway_Name.
Space in the value is also problematic as it makes it show up only partialy.
i.e. for #define Gateway_Name "OpenMQTTGateway One" it only shows "OpenMQTTGateway" as the placeholder.

Steps to reproduce the behavior:

1. Build the firmware (v1.7.0) with WebUI enabled and with MQTT_SERVER, MQTT_PORT, MQTT_USER and Gateway_Name set as empty strings.
2. Configure the gateway
3. Check the MQTT configuration on the WebUI

[github-actions]

This issue is stale because it has been open for 90 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 14 days since being marked as stale.