Vulkan: Fix draw with emulated xfb without xfb active When transform feedback is not active, make sure the code that captures xfb is not generated, even though it's guarded against with an if. This is because no buffer is bound to the capture buffer, and by avoiding generation of code that references that buffer, SwiftShader will not attempt to access the missing descriptor set. Currently, the actual declaration of the buffer is left in the SPIR-V, which seems to be benign. If that causes issues in the future, the SPIR-V transformer can be modified to remove that variable as well. Bug: chromium:1209285 Change-Id: I83da8d1dea5390ecacc681f8ada9f586932deaa4 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3294661 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>