Don't unload source sequence from source monitor when closed in timeline

[Trevor_Asq]

https://drive.google.com/file/d/1nUFBIHX-pckC1agU20YpL2cotRmyeXeU/view?usp=sharing

Current behaviour:

Choose selects sequence and 'open in source monitor'

'Open sequence in timeline' (i.e. displays the source monitor sequence in the timeline)

--- do some stuff---

Close the timeline for the selects sequence

Selects sequence is *unloaded* from the source monitor.

I can't see why that behaviour works for anyone...

Preferred behaviour:

Choose selects sequence and 'open in source monitor'

'Open sequence in timeline' (i.e. displays the source monitor sequence in the timeline)

--- do some stuff---

Close the timeline for the selects sequence

Selects sequence *remains* in the source monitor.