ozone: fix crash when running video decode unittests.

In GLSurfaceOzoneSurfacelessSurfaceImpl::Destroy, if the previous
context was NULL, do not make it current.

BUG=chromium:602921
TEST=Run vda unittests on oak.

Review URL: https://codereview.chromium.org/1887563002

Cr-Commit-Position: refs/heads/master@{#386988}
ui::EglConfigCallbacks GetEglConfigCallbacks(EGLDisplay display) {
  ui::EglConfigCallbacks callbacks;
  callbacks.choose_config = base::Bind(EglChooseConfig, display);
  callbacks.get_config_attribute = base::Bind(EglGetConfigAttribute, display);
  callbacks.get_last_error_string = base::Bind(&ui::GetLastEGLErrorString);
  return callbacks;
}

ui::EglConfigCallbacks GetEglConfigCallbacks(EGLDisplay display) {
  ui::EglConfigCallbacks callbacks;
  callbacks.choose_config = base::Bind(EglChooseConfig, display);
  callbacks.get_config_attribute = base::Bind(EglGetConfigAttribute, display);
  callbacks.get_last_error_string = base::Bind(&ui::GetLastEGLErrorString);
  return callbacks;
}
