Correct the default value of mRequestedInsetsState

The default value of WindowState.mRequestedInsetsState should be the
same as the default value of InsetsController.mState. Previously, the
default value was assigned as the current insets state of the system,
which doesn't reflect the fact about the request.

Bug: 150554206
Test: 1. Reboot the device to lockscreen.
      2. Unlock.
      3. Swipe up from the screen bottom.
Change-Id: If35154358e30b886289e09a6556a444a80c3ce67