Keep track of pending appeared Intent on empty TaskFragment

When the previous pending appeared Intent was cleanup because of launch
failure, we may reuse the same TaskFragment for the next activity start
if the TaskFragment info is not yet received.

In this case, add the new Intent as pending.

Bug: 440507153
Test: atest WMJetpackUnitTests:SplitControllerTest
Flag: EXEMPT small bug fix
Change-Id: Id7240204aad860a04354b841f0ad0c5c7955f813