Comment 3 for bug 1421754

When generating a custom link, any layers that have had their visibility toggled off in the user interface end up with a layeringOrder parameter set to 0 (instead of layering orders defined in the database of 1, 2, and 3). LayeringOrder 0 is used to imply visible:false to
_decodeSingleLayerString().

This is fine. The problem is that an exception is being thrown in the case where none of the requested image layers are deemed to be visible. That is an overreaction.

Removing this exception allows the page to load normally, the appropriate image layer(s) to appear in the image layer accordion user interface, and those with layeringOrder set to 0 to have their visibility toggled off. Toggling an invisible layer back on and then generating a new shareable link confirms that the proper value of layering order is restored (see defined values in `datasources` table of the database).

Testing done on dev instance, pushed to staging server and retested.