Minor fix to attaching stencils

src/gpu/GrRenderTarget.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrRenderTarget.h"
@@ skipping 51 matching lines @@
 
 void GrRenderTarget::onAbandon() {
     SkSafeSetNull(fStencilAttachment);
 
     INHERITED::onAbandon();
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 bool GrRenderTargetPriv::attachStencilAttachment(GrStencilAttachment* stencil) {
+    if (!stencil && !fRenderTarget->fStencilAttachment) {
+        // No need to do any work since we currently don't have a stencil attachment and
+        // we're not acctually adding one.
+        return true;
+    }
     fRenderTarget->fStencilAttachment = stencil;
     if (!fRenderTarget->completeStencilAttachment()) {
         SkSafeSetNull(fRenderTarget->fStencilAttachment);
         return false;
     } 
     return true;
 }