cylc review: Pagination of jobs broken

[wxtim]

Description

I was running Cylc review to look at the output from one of 9 tasks but the task didn't appear on the first page despite it saying entries 1-15 of 21 - the list appeared a bit truncated?

Reproducible Example

[scheduler]
    allow implicit tasks = true
[scheduling]
    [[graph]]
        R1 = fast & slow => end
[runtime]
    [[slow]]
        script = sleep 3600

Run this workflow and examine it in cylc review - there is a mismatch in the tasks shown and the task totals at the bottom of the page.

Cause

This was introduced in https://github.com/cylc/cylc-flow/pull/4897. It's caused by filtering waiting tasks without jobs out using Jinja2 rather than in the Python layer. This means that tasks are not shown, but the totals remain unchanged.