SurfaceFlinger: fix a crash with RefreshRateOverlay

 - Fix a nullptr deference in createLayer
 - Add a test for RefreshRateOverlay

Test: adb shell /data/nativetest64/SurfaceFlinger_test/SurfaceFlinger_test
Bug: 169867983
Change-Id: I496aaeceaa86b55f806ddc921fc5b050417725b7
diff --git a/services/surfaceflinger/tests/Android.bp b/services/surfaceflinger/tests/Android.bp
index 719c46e..b7edb84 100644
--- a/services/surfaceflinger/tests/Android.bp
+++ b/services/surfaceflinger/tests/Android.bp
@@ -34,6 +34,7 @@
         "LayerUpdate_test.cpp",
         "MirrorLayer_test.cpp",
         "MultiDisplayLayerBounds_test.cpp",
+        "RefreshRateOverlay_test.cpp",
         "RelativeZ_test.cpp",
         "ScreenCapture_test.cpp",
         "SetFrameRate_test.cpp",