Fix handling calendar for nonsensical data.

member-fees.scm

@@ -106,6 +106,8 @@
  ;; contain the year in the first cell and 12 cells for months after
  ;; it.
  (define (member-calendar->years-table mc)
+   (if (null? mc)
+       '()
        (let* ((fm (member-calendar-first-month mc))
 	      (lm (member-calendar-last-month mc))
 	      (fy (month-year fm))
@@ -123,7 +125,7 @@
 					(cons (member-calendar-entry->string
 					       (member-calendar-query mc (make-month y m)))
 					      row))))
-		       rows))))))
+			   rows)))))))
 
  ;; Converts the whole calendar into a list of amounts (fees)
  (define (member-calendar->fees mc)