TT#68300 Return from next_page() if the request failed

We should not try to access the data, or decode it as JSON if the
request failed, because in that case the data will not be JSON and
we will get errors from the decoder.

Change-Id: Ibe663992a0487284d79e100b36392534fcbe88db

lib/NGCP/API/Client.pm

@@ -156,6 +156,8 @@ sub next_page {
 
     undef $self->{_collection_url};
 
+    return $res unless $res->is_success;
+
     my $data = $res->as_hash();
     if ($data && ref($data) eq 'HASH') {
         my $new_url = URI->new($data->{_links}->{next}->{href});