Fixed NPE in Task#isResizeableByDockedStack
Fixed NPE in Task#isResizeableByDockedStack

It is possible for the DisplayContent to be null.

Change-Id: I0a85038ae71a24fb5613237d771bc9222dd61cde

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base