Don't save layout if in dont_override.

[iazz]

This simple change ensures that the layout will not be overwritten to user preferences if layout is in dont_override.

A plugin can thus manipulate the config by adding a hook to config_get in order to make the setting of layout temporary. A prime example of a plugin whom this would come in handy is elastic4mobile, which currently overwrites the layout setting, as reported in #8403. A PR for that plugin is coming shortly.

[iazz]

PR thomascube/roundcube-elastic4mobile#8 is submitted to make use of that change.

[alecpl]

Please add { }. Also, what about the other lines of code around? Should set_env() still be invoked? Should $cols be set?

[iazz]

The initial issue that I'm trying to fix here is that the elastic4mobile plugin resets the layout in user preferences every time the user accesses their account from a mobile device. If a user normally uses, say, the Larry skin with the list layout, as soon as they access the webmail using a mobile browser, the temporarily used Elastic skin resets the layout to widescreen in a permanent fashion. When the user logs back using a desktop browser, the layout is widescreen and has to be changed in preferences back to list.

The thing is that elastic4mobile is a hack that temporarily overrides the skin to Elastic when the requesting browser is in mobile mode. Further down the road, the currently used skin can change the layout if the current layout is not actually supported by the skin (which is the case with Elastic, which supports only widescreen). All the rest seems to work just right, (calls to set_env(), setting of $cols, and whatnot) except that the layout setting is saved to the user's preferences.

So it seems reasonable to leave everything else as is and only prevent overwriting of the layout preference when it is found in dont_override. On the plugin side, elastic4mobile must simply add layout to dont_override in a config_set hook, and do this for every request (including AJAX), so that the layout preference doesn't update the saved user preferences.