queue2: Fix average input rate calculation on small input range

queue2: Fix average input rate calculation on small input range

When dealing with small-ish input data coming into queue2, such as
adaptivedemux fragments, we would never take into account the last
<200ms of data coming in.

The problem is that usually on TCP connection the download rate
gradually increases (i.e. the rate is lower at the beginning of a
download than it is later on). Combined with small download time (less
than a second) we would end up with a computed average input rate
which was sometimes up to 30-50% off from the *actual* average input
rate for that fragment.

In order to fix this, force the average input rate calculation when
we receive an EOS so that we take into account that final window
of data.

https://bugzilla.gnome.org/show_bug.cgi?id=768649