- set an empty value for clicked buttons without a value

- see gisle/html-form#7

Author: Sadrak

lib/HTML/Form.pm

@@ -1426,6 +1426,7 @@ sub form_name_value
 {
     my $self = shift;
     return unless $self->{clicked};
+    $self->value("") unless defined $self->value;
     return $self->SUPER::form_name_value(@_);
 }