tests: Initialize fields so test does not crash.

I had forgotten to define the LD_LIBRARY_PATH and VK_LAYER_PATH
environment variables in VS2015 before running the tests. The
test crashed when it tried to delete the un-initialized pointers.
I have added a default initialization to VK_NULL_HANDLE so you
get an error message instead of a crash.

Change-Id: Ia8e2770914d10dc67be744e418dafe82cc164d67
1 file changed