Make non-invalidating patch request ordering deterministic.

[garretrieger]

Currently the order of fetches for invalidating patches is deterministic (https://w3c.github.io/IFT/Overview.html#invalidating-patch-selection), however for non-invalidating patches we don't specify any specific ordering, relevant text:

"Otherwise select exactly one of the entries in no invalidation entry list. The criteria for selecting the single entry is left up to the implementation to decide."

We should make this selection deterministic, the simplest approach would be to use the patch map entry order (ie. select the patch associated with the patch map entry which occurs first). We'll want to note that this does not prevent parallel requests, only that the initiation order for those requests should follow the specified ordering.