Bad warning when no engine specified

If you try to

$config = graphapi_default_config();
$element[0]['relation']['graph']['#markup'] = theme('graphapi_dispatch', array('graph' => $relation_graph, 'config' => $config));

Then your $config is missing the ['engine'] component, and the graph will fail. Unfortunately, the wrong error is given: "No Graph API render engines enabled. Check your !modules_page for a Graph API render engine.", even if there ARE engines enabled.

Here is a patch for the correct message logic (and also a grammatical mistake).

I would also think it would make sense to choose an engine in the default settings, if one is available, but I thought there might be some reason you don't do that, so I left it out.