AudioPolicyManager: voice call routing fail safe

Bug: 298609303
Test: make

When devices involved in a call are disconnected, since APM
does not expect such cases, assertion happens.
This CL allows to fail safe on voice call routing.

Change-Id: I14b1ec245e640eeae14390ea62d93a4bdfe5bade
Signed-off-by: François Gaffie <francois.gaffie@renault.com>