Vulkan: Don't wait on unflushed sync objects without a Context The app "Car Parking Multiplayer" issues a ClientWaitSync() command without having already flushed the sync object and without an active context. We should return TIMEOUT immediately rather than attempting to wait on the sync object, since we can't flush it and it'll never be signalled. Bug: angleproject:5613 Bug: angleproject:5656 Test: MultithreadingTest.NoFlushNoContextReturnsTimeout Change-Id: Ieaf675ca9144f9c851c73b9ca399daaf4ed1cd0f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2693375 Commit-Queue: Tim Van Patten <timvp@google.com> Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com>