SurfaceFlinger: always consider layers with setFrameRate

If an app called to setFrameRate on a layer, consider it when choosing
the refresh rate, even if the layer has posted buffers.

Bug: 152411921
Test: adb shell /data/nativetest64/libsurfaceflinger_unittest/libsurfaceflinger_unittest
Change-Id: I01f139b34cee01255693ed274225e79d83b0f894