fixup auto-check single options

fulcrm_shoppingcart.module

@@ -582,6 +582,7 @@ function fulcrm_shoppingcart_buy_eventbookingtype_form( $form, &$form_state, $pe
             $form[ 'eventslots' ][ $eventpart_key ] = array( '#type' => 'radios',
                                                              '#title' => $eventparts[ $eventpart_id ][ 'name' ],
                                                              '#options' => array(),
+                                                             '#required' => TRUE,
                                                              );
         $eventslot_id = fulcrm_crypto_object_id_form_value( 'eventslot.id', $eventslot[ 'id' ] );
         $remaining_capacity = $eventslot[ '_remaining_capacity' ];
@@ -590,10 +591,10 @@ function fulcrm_shoppingcart_buy_eventbookingtype_form( $form, &$form_state, $pe
     }
 
     $choices = false;
-    foreach ( $form[ 'eventslots' ] as $eventpart_id => $eventpart ) {
-        if ( count( $eventpart[ '#options' ] ) == 1 ) {
-            foreach ( $eventpart[ '#options' ] as $option_key => $option_value )
-                $eventpart[ '#default_value' ] = $option_key;
+    foreach ( $form[ 'eventslots' ] as $eventpart_id => $eventpart_form ) {
+        if ( count( $eventpart_form[ '#options' ] ) == 1 ) {
+            foreach ( $eventpart_form[ '#options' ] as $option_key => $option_value )
+                $form[ 'eventslots' ][ $eventpart_id ][ '#default_value' ] = $option_key;
         } else {
             $choices = true;
         }