Fixing regression in what is considered a restart attempt

- CTS tests can start activities directly in the pinned stack with the
  CLEAR_TASK and NEW_TASK flags, so this check should only consider it
  a restart attempt if mReusedTask is set, as in
  setTaskFromIntentActivity(), otherwise the newly started activity
  will be triggered back into fullscreen.

Bug: 37501224
Test: android.server.cts.ActivityManagerPinnedStackTests
Change-Id: Ia37f9d77bfb85882e50271300234bfc6c2969f9a