`renderFilter` adds `filter=` to URL many times

[CSchank]

In IHP v1.3.0, this was not a problem. If you used the pagination function renderFilter and submitted the form more than once, it would overwrite the filter parameter in the URL. However, in IHP v.1.4.x it keeps adding multiple filter parameters to the URL over and over. This causes the filtering not to work. Since the renderFilter function hasn't changed, I think it may be related to this: ad872d5 somehow.