Only the instructions following a return statement were being marked as
affected by it so predication would be applied. But in a loop the instructions
above the return statement are also affected by it.

Bug b/25220690

Change-Id: If2490a6e0b4e9cf8b6e28b33cbbbcec8b4ebfdaa
Reviewed-on: https://swiftshader-review.googlesource.com/5183Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>