Avoid segfault when there is no "laptop_panel" capable device
Avoid segfault when there is no "laptop_panel" capable device

When no device is found rather than returning an error the function
hal_manager_find_by_capability returns an array with a single NULL value in
it.

This is part of the fix for MB: #1607

meego-netbook-ux/meego-panel-devices,meego-netbook-ux/meego-panel-devices,meego-netbook-ux/meego-panel-devices