Imagine the following situation:

1. Clear draw framebuffer
2. Noop operation on the framebuffer (Clear, ClearBuffer,
   BlitFramebuffer with flags specifying non-existing attachments)
3. Change framebuffer's attachment
4. Draw into framebuffer

At step 2, FramebufferVk::syncState was called before noop-ing the
operation.  During syncState, deferred clears were stored in the
framebuffer and weren't flushed because the actual operation was not
performed.

At step 4, the deferred clear meant for the prior attachment gets
applied to the new attachment.

Bug: angleproject:4865
Change-Id: I5b096bacf00356b4dccd4cbc9561b87b1bb557d8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2309224Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>