Fix potentially uninitialized variables.

Bug 15387371

Change-Id: Ie0486feeebc6e4bceba148bea69f2d1ee1d1ffd8
Reviewed-on: https://swiftshader-review.googlesource.com/4499
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>