Do not notify of WIFI to LTE handover for disconnected call.

It is possible for the onCallHandover callback to indicate that a
call in the process of disconnecting or which has been disconnected already
has handed over from WIFI to LTE.  We suppress the connection event if this
is the case.

Test: Reproduced bug, and then confirmed fix corrects the issue.
Bug: 65490850
Change-Id: I460db6c122188d9bd9a4db4e93cee44bf9c63905