add some error handling for studygroup csv report

booking.studygroups_report.inc

@@ -19,8 +19,7 @@ function booking_studygroups_csv_report($group_id) {
 						array(':eid' => $event->eid, ':sid' => $group_id))
 			->fetchObject();	
 			
-	if (! $group)
-	{
+	if (! $group) {
 		drupal_set_message("Error: Could not find matching study group ID. Unable to view group membership.", 'error', FALSE);
 		drupal_goto('admin/booking/studygroups');
 		return "";			
@@ -66,9 +65,14 @@ function booking_studygroups_csv_report($group_id) {
     }    
     //add the spaces and put this element in the right array
     $data[$member->booking_session_id][] = implode(' ', $text);
-
   }
   //watchdog('booking_debug', "<pre>Study Group CSV Report\n@info</pre>", array('@info' => print_r( $data_array, true)));
+
+  // Check if we had no data added, that means there were no people in this study group
+  if (empty($data)) {
+		drupal_set_message("Error: Study group $group_id has no people assigned.", 'error', FALSE);
+		return "";
+  }
   
   //calculate the CSV layout
   $header_array = array_keys($data);