allow undef filename when Content header is present

Author: simbabque

Changes

@@ -5,6 +5,8 @@ Change history for HTML-Form
     - Allow buttons to not have a value (GH#8) (Felix Ostmann and Julien Fiegehenn)
     - The legacy API of FileInput fields now correctly supports setting a
       custom filename (GH#10) (Gil Magno and Julien Fiegehenn)
+    - Allow undef filename for FileInput if there is a Content header (GH#30)
+      (Julien Fiegehenn)
 
 6.07      2020-02-21 03:50:52Z
     - Restore =head1 NAME section to pod for HTML::Form

lib/HTML/Form.pm

@@ -1539,7 +1539,8 @@ sub form_name_value {
     my $filename = $self->filename;
     my @headers = $self->headers;
     my $content = $self->content;
-    if (defined $content) {
+    my %headers = @headers;
+    if (defined $content || grep m/^Content$/, keys %headers) {
 	$filename = $file unless defined $filename;
 	$file = undef;
 	unshift(@headers, "Content" => $content);