Adjusted glm_get_header() to break less

Adjusted glm_get_header() to break less

This function wasn't always doing its expected behavior. Now it
properly checks for image data failures at any step and applies
classes to the featured image based on which image it actually
displays. e.g. if it passes into member detail but fails to get an
image from the member it gets the 'member-default' class, unless
there is no default member image, in which case it gets the
'wp-default' class.