Start a visible requested activity if still in initializing state

A non-top activity was set to visible before real starting it and
therefore prevented the activity from being started next time
while computing visibility.

This happens in split-screen mode where the two split activities
were both paused while several translucent activities were
started consecutively to a fullscreen task on top. The visibility
of the translucent activities in the top fullscreen task was set
to true while one of the activities paused, but was unable to
start since not all pausing activity completed. After all
activities completed pausing, only the top-most activity was
started.

Bug: 227658778
Test: start bookmark pages on Chrome while in split
Change-Id: I18a3a017d03225d421ffe955504e7336322d4a16