Perform the minimal dimension restrictions on leaf Task

The minimal dimension restrictions ensure the leaf task fragment
won't be displayed too small to manipulate. However, the out bounds
was exceed the parent task bounds and resulted in wrong inset
calculation while layouting the window.

Restore performing the minimal dimension restrictions in leaf tasks
(the behavior before f5623157).

Bug: 193493038
Test: wm presubmit
Change-Id: Ide7ef2ee0b5fd2d6de353a1e9365a7120b2ab0d3