cvsimport: do not barf on creation of an empty file.

When the server says "created this file whose length is empty",
we mistakenly said "oops, the server did not say a sensible
thing".  Fix it.

Spotted and fixed by Linus, acked by Martin.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-cvsimport.perl

@@ -371,7 +371,7 @@ sub file {
 }
 sub _fetchfile {
 	my ($self, $fh, $cnt) = @_;
-	my $res;
+	my $res = 0;
 	my $bufsize = 1024 * 1024;
 	while($cnt) {
 	    if ($bufsize > $cnt) {