Camera: Check consumer interface before disconnecting

The internal buffer queue and respective 'mConsumer' may
never get initialized in case the connection and/or
configuration of client shared output surfaces fails.
To avoid possible instabilities check whether the
consumer interface is valid before trying to disconnect.

Bug: 143506890
Test: atest
cts/tests/camera/src/android/hardware/camera2/cts/MultiViewTest.java

CRs-Fixed: 2540327

Change-Id: Ia533233444fd548ddb52f4fde06212a21bc843bc
(cherry picked from commit 359adca4b7cf734ab9a0d27a005b9f6dfdc0ad8e)