dpkg-source: Fix "uninitialized value" warning

ChangeLog

@@ -2,6 +2,9 @@
 
 	* configure.ac: Release 1.14.16.1
 
+	* scripts/dpkg-source.pl: Fix "uninitialized value"
+	warning.
+
 	* debian/control: Add libtimedate-perl to
 	dpkg-dev's Depends and to Build-Depends (for
 	build-time tests). This introduces our first

scripts/dpkg-source.pl

@@ -771,7 +771,7 @@ if ($opmode eq 'build') {
     open(DSC, ">:utf8", "$basenamerev.dsc") ||
         syserr(_g("create %s"), "$basenamerev.dsc");
 
-    $substvars->parse($varlistfile) if -e $varlistfile;
+    $substvars->parse($varlistfile) if $varlistfile && -e $varlistfile;
     tied(%{$fields})->set_field_importance(@dsc_fields);
     tied(%{$fields})->output(\*DSC, $substvars);
     close(DSC);