Only skip transfer starting window if orientation is not undefined.

Allow transfer starting window to next activity if the requested
orientation is changed at runtime, because configuration change will
trigger rotation transition.
Only disallow transfer starting window if the requested orientation
is pre-defined with specific orientation, since there won't have
rotation transition.

Flag: EXEMPT bugfix
Bug: 379534938
Test: launch two activities to simulate transfer starting window in
opening transition with
A. set orientation at runtime and
B. pre-define orientation in manifest.
Verify no flicker for both case.

Change-Id: I84bf8f5bf6c2f553636d4fb890cfa5db0995e7d2