The checks and call to contextVk->flushImpl() needs to be moved before
the timeout check to ensure that the vkEvent is flushed to HW eventually
when the caller is waiting on it, even if they don't specify a timeout.

Bug: chromium:1060139
Test: CopyOutputScalingPixelTest.ScaledCopyOfDrawnFrame/48
Change-Id: I725ea492aaf21e291fe3e5b9ae11ea009e59e019
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2640423
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Alexis Hétu <sugoi@chromium.org>