Vulkan: SPIR-V Gen: Fix conditionals with pruned blocks Rewored the visitIfElse function to simplify the logic and correctly handle if-else constructs where the true block is pruned. Bug: angleproject:4889 Change-Id: Ib968a2fe65f4b6463158fd76e7d67757115ee832 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3046101 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>