Vulkan: Fix synchronization with current surface
Vulkan: Fix synchronization with current surface

Since a6242e4d4 ("Vulkan: Support submitting multiple semaphores"),
semaphores are not generated because the function generating checks for
non-empty command graph right after flushing.

Bug: angleproject:3492

Change-Id: I03db4a77fe24fdfdf39ba535b235451ae0275a0e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1638579
Reviewed-by: Cody Northrop <94770d7fe1cce6ea0791fa9927c1107de4d2e37b@google.com>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Michael Spang <e1fb1a05abba8fb04acbcbe6d766da7764320db0@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle