debian: Do not backup nonexistent database files

The arch database only exists if the user has more than one architecture
configured.

Closes: #745592, #745651

debian/changelog

@@ -1,6 +1,7 @@
 dpkg (1.17.8) UNRELEASED; urgency=low
 
-  *
+  * Do not backup nonexistent database files from the cron.daily file.
+    Closes: #745592, #745651
 
  -- Guillem Jover <guillem@debian.org>  Mon, 21 Apr 2014 17:59:10 +0200
 

debian/dpkg.cron.daily

@@ -16,6 +16,7 @@ if cd /var/backups ; then
     done
     if [ "$dbchanged" = "yes" ] ; then
         for db in $dbfiles ; do
+            [ -e $dbdir/$db ] || continue
             cp -p $dbdir/$db dpkg.$db
             savelog -c 7 dpkg.$db >/dev/null
         done