Fix root RenderNode damage calculation

 Bug: 15888445

Change-Id: I281ec9271c9889673dcdfcb6d31e341a7b47b7de
diff --git a/libs/hwui/renderthread/CanvasContext.cpp b/libs/hwui/renderthread/CanvasContext.cpp
index 57279b7..a4ac262 100644
--- a/libs/hwui/renderthread/CanvasContext.cpp
+++ b/libs/hwui/renderthread/CanvasContext.cpp
@@ -185,6 +185,11 @@
     } else if (!mDirtyRegionsEnabled || mHaveNewSurface) {
         dirty.setEmpty();
     } else {
+        if (!dirty.intersect(0, 0, width, height)) {
+            ALOGW("Dirty " RECT_STRING " doesn't intersect with 0 0 %d %d ?",
+                    SK_RECT_ARGS(dirty), width, height);
+            dirty.setEmpty();
+        }
         profiler().unionDirty(&dirty);
     }