cvsimport: catch error condition where cvs host disappears

Add error handling for cases where the cvs server goes away unexpectedly.
While I don't know why the cvs server is so erratic, we should definitely
exit here before committing bogus files.

Signed-off-by: Martin Langhoff <martin@catalyst.net.nz>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-cvsimport.perl

@@ -337,6 +337,10 @@ sub file {
 	}
 	close ($fh);
 
+	if ($res eq '') {
+	    die "Looks like the server has gone away while fetching $fn $rev -- exiting!";
+	}
+
 	return ($name, $res);
 }