Fix partial replace head tracking

[marutypes]

This PR fixes partial replaces inadvertently triggering head asset updates. This was usually not causing issues, but in some cases could break stuff.

I should note that this was partially to blame for the spike in url.absolute errors. Submitting a remote form would call:

        Page.refresh
          response: xhr
          onlyKeys: @refreshOnSuccess

Page.refresh would then trigger

    options.partialReplace = true
    options.onLoadFunction = callback

    xhr = options.response
    delete options.response
    Turbolinks.loadPage null, xhr, options

Which would then try to update the head assets, with an error callback that looked like:

onHeadUpdateError = ->
          Turbolinks.fullPageNavigate(url.absolute)

Where url is null.

Preventing head asset updates on partial request should fix the new instances of this error that all occurred with a tg-remote related last event.

The old instances of this error are a bit more insidious and will be addressed in an upcoming PR.

[qq99]

your logic changes LGTM
My only comment would be that I prefer the style of explicit if/else rather than return throughout to terminate control flow

[GoodForOneFare]

Makes sense 👍

[marutypes]

I'll 🚢 this when it's done on CI

[marutypes]

Had to rebase on top of the other two prs