Disable task snapshot when image size is invalid

Since devices such as IoT can have no screen, the size of
graphic buffer can be 1x1. In this case the WindowManager crashes
while making bitmap with reduced size.
To prevent the crash, disabled snapshotting on this screen.

This may also happen on phones sporadically.

Bug: 62401135
Fixes: 64733031
Test: Device without the display does not crash when app dies.
Change-Id: I367008405e6238baf3e56974f7d363ea81dfa916
(cherry picked from commit 9035d72c)