[backend] also send trailing '0' bytes in 8192 byte boundaries

src/backend/BSServer.pm

@@ -663,7 +663,7 @@ sub reply_receiver {
   $replying = 2 if $chunked;
   while(1) {
     my $data = BSHTTP::read_data($hdr, 8192);
-    last unless $data;
+    last unless defined($data) && $data ne '';
     $data = sprintf("%X\r\n", length($data)).$data."\r\n" if $chunked;
     swrite($data);
   }