SurfaceFlinger: check pending fence when set active config is pending

ag/9653007 moved performSetActiveConfig() after the check for whether
previous frame was missed or not. This creates a logical loop with the
inactivity timer logic as the timer is reset while we try to change
the active config.

Bug: 152321942
Test: trigger refresh rate and observe refresh rate
Change-Id: I081ef8123ed46b979eae804a47c4d06491df877c