Fix crash for cross-process embedding

1. For TaskFragment#isAllowedToBeEmbeddedInTrustedMode, it should return
   false if any child activity is not in trusted mode.
2. We don't need to check requested bounds if it is empty.

Bug: 197364677
Test: atest WmTests:TaskFragmentTest
Change-Id: Ic9eab24f6e8530c03910e4ffaeeb6d3b69591ec7