MSAN detected uninitialized memory which caused many test failures.
This can be easily fixed by zeroing out the memory before calling
XCreateImage.

Change-Id: I913c818ef38446055af7fd6aa885028e5f3f8bfb
Reviewed-on: https://swiftshader-review.googlesource.com/12388Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>