piwigo-openstreetmap 15.d saves incorrect CSS "autopx"

[jbd7]

Issue

The plugin admin form to configure the map generates incorrect CSS.

Steps to reproduce

• Enable OSM plugin
• Load plugin settings page in Piwigo
• Find the parameter Map width : in px or auto
• Enter nothing: Error, the form won't save
• Enter auto and the plugin saves settings
• The map is displayed on the front end with an incorrect CSS width: autopx;