fix some aspects of [2258746] native crash in launcher2

Surface::validate() could sometimes dereference a null pointer before checking it wasn't null.
This will prevent the application to crash when given bad parameters or used incorrectly.
However, the bug above probably has another cause.
diff --git a/include/ui/Surface.h b/include/ui/Surface.h
index 70303cd..008c297 100644
--- a/include/ui/Surface.h
+++ b/include/ui/Surface.h
@@ -109,7 +109,7 @@
 
     ~SurfaceControl();
 
-    status_t validate(SharedClient const* cblk) const;
+    status_t validate() const;
     void destroy();
     
     sp<SurfaceComposerClient>   mClient;
@@ -190,7 +190,7 @@
 
     status_t getBufferLocked(int index, int usage);
    
-           status_t validate(SharedClient const* cblk) const;
+           status_t validate() const;
 
     inline const GraphicBufferMapper& getBufferMapper() const { return mBufferMapper; }
     inline GraphicBufferMapper& getBufferMapper() { return mBufferMapper; }