The buffer changes ownership after queuing it, so unlock it first.
The decRef() gets removed in a subsequent patch.

Bug b/34981145

Change-Id: I4710699af46a7cbde12e97bc444ad35747509b07
Reviewed-on: https://swiftshader-review.googlesource.com/8848Reviewed-by: Greg Hartman <ghartman@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Greg Hartman <ghartman@google.com>