Don't scroll to live content on initial content load

When going from edit mode -> GH, we save the scroll position and restore
it. In this case, we should not immediately scroll away from the restored
scroll position. This change avoids scrolling on the initial content
load, and only scrolls on subsequent content changes.

Fixes: 357977239
Test: enter/exit edit mode with music playing
Flag: com.android.systemui.communal_hub
Change-Id: I5f846d5b12a7f416326c8a9cef5806bc5b00f09f