Can't reduce an empty list with the max function.

The max function requires at least 1 argument to be given, and in the
case where we have no table to load it then fails badly, as show here:

  CL-USER> (handler-case
               (reduce #'max nil)
             (condition (c)
               (format nil "~a" c)))
  "invalid number of arguments: 0"

Of course Common Lisp comes with a very easy way around that problem:

  CL-USER> (reduce #'max nil :initial-value 0)
  0

Fix #381.

src/utils/schema-structs.lisp

@@ -322,7 +322,8 @@
   "Count how many indexes maximum per table are listed in SCHEMA."
   (reduce #'max (mapcar #'length
                         (mapcar #'table-index-list
-                                (schema-table-list schema)))))
+                                (schema-table-list schema)))
+          :initial-value 0))
 "Count how many indexes maximum per table are listed in SCHEMA."
 
 (defmethod max-indexes-per-table ((catalog catalog) &key)