Better empty context handling.

I believe this may be fixed by #1263896: "context exists" access plugin broken (patch) instead?

Crosslinking 2 other issues with nearly the same patch. We should really consolidate that.

The 6 year old patch in #6 does not apply to the latest ctools 7.x-1.x-dev.

Checking patch includes/context.inc...
Hunk #1 succeeded at 1416 (offset 422 lines).

Checking patch includes/context.theme.inc...
Hunk #1 succeeded at 215 (offset -1 lines).

Checking patch views_content/plugins/relationships/view_from_argument.inc...
error: while searching for:
  $name = $conf['name'];
  list($plugin, $view_data) = explode(':', $name);
  list($view_name, $display_id) = explode('-', $view_data);
  $keys = array_keys($conf['context']);

  if (empty($contexts[$keys[0]]->data)) {
    return ctools_context_create_empty('view', NULL);
  }

  // Load our view up.
  $data = views_get_view($view_name);
  if ($data) {
    // Set the display.
    $data->set_display($display_id);
    $context_keys = array_keys($contexts);
    foreach ($data->display_handler->get_argument_input() as $id => $argument) {
      if ($argument['type'] == 'context') {
        $key = array_shift($context_keys);
        if (isset($contexts [$key])) {
          if (strpos($argument['context'], '.')) {
            list($context, $converter) = explode('.', $argument['context'], 2);
            $args[] = ctools_context_convert_context($contexts[$key], $converter, array('sanitize' => FALSE));
          }
          else {
            $args[] = $contexts[$key]->argument;
          }
        }
      }
    }
    // remove any trailing NULL arguments as these are non-args:

error: patch failed: views_content/plugins/relationships/view_from_argument.inc:58
error: views_content/plugins/relationships/view_from_argument.inc: patch does not apply

I committed #2399313: Relationship silently left out if it has optional required context so this needs another reroll. Also that might have helped solve part of what this patch is trying to do.

Reroll the patch.