[WWcvs] pg: Prevent the empty list from having open and close be set to 'start'

[dpvc v. a. <we...@ma...>]

Log Message:
-----------
Prevent the empty list from having open and close be set to 'start'
(a value used internally).

Modified Files:
--------------
    pg/lib/Parser:
        List.pm

Revision Data
-------------
Index: List.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Parser/List.pm,v
retrieving revision 1.16
retrieving revision 1.17
diff -Llib/Parser/List.pm -Llib/Parser/List.pm -u -r1.16 -r1.17
--- lib/Parser/List.pm
+++ lib/Parser/List.pm
@@ -44,6 +44,7 @@
       else {$equation->Error(["Entries in a %s must be of the same type",$type->{name}])}
     }
   }
+  $open = '' if $open eq 'start'; $close = '' if $close eq 'start';
   $list = bless {
     coords => $coords, type => $type, open => $open, close => $close,
     paren => $paren, equation => $equation, isConstant => $constant