Correctly call glviewport when surface changes.

Change-Id: I7ef1539e39ea67245bac5ee410deb5918fc5dfcf
diff --git a/libs/rs/rsContext.cpp b/libs/rs/rsContext.cpp
index 8798612..1932108 100644
--- a/libs/rs/rsContext.cpp
+++ b/libs/rs/rsContext.cpp
@@ -446,6 +446,7 @@
 
     if (mWidth && mHeight) {
         mStateVertex.updateSize(this);
+        mFBOCache.updateSize();
     }
 }