Fix for DEPS roll failure (a patch to r9898)



git-svn-id: http://skia.googlecode.com/svn/trunk@9901 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index 3cf596b..78220c0 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1131,6 +1131,10 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 void GrContext::flush(int flagsBitfield) {
+    if (NULL == fDrawBuffer) {
+        return;
+    }
+
     if (kDiscard_FlushBit & flagsBitfield) {
         fDrawBuffer->reset();
     } else {