Vulkan: Fix crash in SPIR-V transform with varying precision fix Bug: angleproject:386749841 Change-Id: I5743eb049dde6c8a093b175e857251bad9b2bc9a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6232948 Commit-Queue: Cody Northrop <cnorthrop@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com>