Handle isUsbDataSignalingEnabledForUser PO case

If there is no DO or COPE PO, then
usb data signaling is enabled.

Bug: 180547881
Test: Manual testing
      atest com.android.server.devicepolicy.DevicePolicyManagerTest
Change-Id: I32a1f73ca403b6c1c38b7c6fa70cc2f0f0830324