Fix two notices in commons_events

These two kept on showing up...

Notice: Undefined index: attendee_count in theme_commons_events_attending_event() (regel 13 van ..../profiles/commons/modules/commons/commons_events/includes/commons_events.theme.inc).

Notice: Undefined index: #items in commons_events_entity_view_alter() (regel 205 van ..../profiles/commons/modules/commons/commons_events/commons_events.module).

This patch silences them...

The second notice was also reported in #2157897: Warning: Invalid argument supplied for foreach() in element_children()