Don't call finish on GrDrawTarget if we drew no batches

src/gpu/GrDrawTarget.cpp

Index: src/gpu/GrDrawTarget.cpp
diff --git a/src/gpu/GrDrawTarget.cpp b/src/gpu/GrDrawTarget.cpp
index d03130d18e87564625cb95346fee78293857d062..717cd5d1bb9f109425730cc4e4df6e109347f10c 100644
--- a/src/gpu/GrDrawTarget.cpp
+++ b/src/gpu/GrDrawTarget.cpp
@@ -216,6 +216,9 @@ void GrDrawTarget::prepareBatches(GrBatchFlushState* flushState) {
 }
 
 void GrDrawTarget::drawBatches(GrBatchFlushState* flushState) {
+    if (0 == fRecordedBatches.count()) {
+        return;
+    }
     // Draw all the generated geometry.
     SkRandom random;
     GrRenderTarget* currentRT = nullptr;