Minimize state changes when updating layers

Change-Id: I407fcc80bd3178f9f09a3b379ceb7f7ce0749e08
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index 1de0f9d..edb4c10 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -378,6 +378,9 @@
     if (scissorEnabled && (x != mScissorX || y != mScissorY ||
             width != mScissorWidth || height != mScissorHeight)) {
 
+        if (x < 0) x = 0;
+        if (y < 0) y = 0;
+
         glScissor(x, y, width, height);
 
         mScissorX = x;