Fix crash recording broadcast receiver duration

Edge case: when a broadcast is skipped outright (e.g. because the recipient
app had just crashed) the which-receiver-is-current bookkeeping is not
initialized.  That means we can't trust it for array-indexing.

Test: atest com.android.cts.devicepolicy.ManagedProfileTest
Change-Id: Id27ddea2e241dbddf34da6a7bab7997f5d9c5070