Viewer.getState - add more info in error when no source

[emoen]

In Viewer.js - getState -
...
if (!source) {
throw new Error("Could not find source for layer '" + record.get("name") + "'");
}

should be more verbose if eg. layer is a OpenLayers.Layer.Vector. Replace with something like:
throw new Error("Could not find source for record '" + record.get("name") + " and layer" + layer.name + "'");

[emoen]

Also OpenLayers.Layer.Vector has no source so can be skipped - by replacing
if (layer.displayInLayerSwitcher ) {
with
if (layer.displayInLayerSwitcher && !(layer instanceof OpenLayers.Layer.Vector) ) {

[ahocevar]

Thanks for the bug report @emoen. Would you be able to provide a pull request?