[interchange] Fix potential "use of uninitialized value" if called during startup

[David Christensen]

commit af6e71231e72eb42b88d4100b500e3d34e5a2adc
Author: David Christensen <david at endpoint.com>
Date:   Thu Jun 22 14:38:50 2017 -0500

    Fix potential "use of uninitialized value" if called during startup

 lib/Vend/File.pm |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/lib/Vend/File.pm b/lib/Vend/File.pm
index 386ed74..6d9d4ee 100644
--- a/lib/Vend/File.pm
+++ b/lib/Vend/File.pm
@@ -707,10 +707,13 @@ sub allowed_file {
 	my $fn = shift;
 	my $write = shift;
 	my $status = 1;
+	my $pat;
 	$Vend::File::errstr = '';
 	if(	$Global::NoAbsolute
 			and
-		$fn !~ $Global::AllowedFileRegex->{$Vend::Cat}
+		$pat = $Global::AllowedFileRegex->{$Vend::Cat // ''}
+			and
+		$fn !~ $pat
 			and
 		absolute_or_relative($fn)
 		)