[Cherry-pick] Use the correct handleMmi function

In the event that the PhoneAccountHandle is null, do not pass in null as
the account handle, instead use the handleMmi string that only takes the
dialString.

This change seems to have taken place in
http://ag/#/c/838273/11/src/com/android/dialer/util/TelecomUtil.java
Fixing that with this CL

Bug:31165762
Bug:29443147
Change-Id: Idc174639c48ab3c01ad5bde340272a8ec55d6ab1
(cherry picked from commit f9163d84e77a5287c16c679a946c3a8f934350d1)