Minor fix to attaching stencils

src/gpu/GrRenderTarget.cpp

Index: src/gpu/GrRenderTarget.cpp
diff --git a/src/gpu/GrRenderTarget.cpp b/src/gpu/GrRenderTarget.cpp
index c16738e795d8d1698609b5d9c64f2a0a323780f1..4bb01432cec6f0937f4bf9d1f9659917c1f6e832 100644
--- a/src/gpu/GrRenderTarget.cpp
+++ b/src/gpu/GrRenderTarget.cpp
@@ -69,6 +69,11 @@ void GrRenderTarget::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);