Do not emit WTF if there is no delegate

WTF should only be logged when there is more than one delegates,
not when there is none.

Test: atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testKeyManagement
      and check logcat for the absence of WTF logs
Bug: 122363826

Change-Id: I51972ec4fabb2de70a6fe1700afae3aea95e34ab