[interchange] In carts, provide prevention for item attributes migrating to other items

commit 01b3df9d13b58d2a4ee9c146eac176df10fdefb1
Author: Josh Lavin <[email protected]>
Date:   Thu Mar 13 13:42:52 2014 -0700

    In carts, provide prevention for item attributes migrating to other items
    
    This can happen due to a user's removal of an item and subsequent use of Back button.
    
    Requires setting of CGI parameter in ord/basket.html and other cart modification pages:
    <input type="hidden" name="mv_nlines" value="[nitems lines=1]">
    
    By Mike Heins.

 lib/Vend/Order.pm |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/lib/Vend/Order.pm b/lib/Vend/Order.pm
index 11d8afd..5944598 100644
--- a/lib/Vend/Order.pm
+++ b/lib/Vend/Order.pm
@@ -22,6 +22,7 @@
 # MA  02110-1301  USA.
 
 package Vend::Order;
+use Vend::Error;
 require Exporter;
 
 $VERSION = '2.110';
@@ -2063,6 +2064,15 @@ my @Scan_modifiers = qw/
 sub update_quantity {
     return 1 unless defined  $CGI::values{"quantity0"}
 		|| $CGI::values{mv_quantity_update};
+
+	if ( my $n = $CGI::values{mv_nlines} ) {
+		my $check = scalar(@$Vend::Items);
+		if ( $n != $check ) {
+			Vend::Error::interaction_error();
+			return undef;
+		}
+	}
+
 	my ($h, $i, $quantity, $modifier, $cart, $cartname, %altered_items, %old_items);
 
 	if ($CGI::values{mv_cartname}) {