Only call context::unMakeCurrent() if context is changed. Bug: angleproject:5509 Change-Id: Ifbc6aa23a218498c5e2f6a094296045b2d5dfacf Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2633421 Commit-Queue: Peng Huang <penghuang@chromium.org> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>