Filtering null emissions from the long-press effect StateFlow.

The null values of the actionType flow only represent an idle state
where nothing happens. It is not necessary to collect them and add
coroutine continuation points just for this values.

Test: presubmit
Flag: ACONFIG quick_settings_visual_haptics_longpress TEAMFOOD
Bug: 333987986
Change-Id: I9219deb2cfb77c8a7fb8306c4a7879b767d0a0a4