Make SkRWBuffer destruct safely

tests/DataRefTest.cpp

Index: tests/DataRefTest.cpp
diff --git a/tests/DataRefTest.cpp b/tests/DataRefTest.cpp
index f1e645ec7e7cbac855b5bc9de44ca664384cdec4..a474019e925044246c754b7e5538a7d36cde190b 100644
--- a/tests/DataRefTest.cpp
+++ b/tests/DataRefTest.cpp
@@ -328,3 +328,10 @@ DEF_TEST(RWBuffer_size, r) {
     REPORTER_ASSERT(r, !iter.next());
     REPORTER_ASSERT(r, 0 == iter.size());
 }
+
+// Tests that it is safe to destruct an SkRWBuffer without appending
+// anything to it.
+DEF_TEST(RWBuffer_noAppend, r) {
+    SkRWBuffer buffer;
+    REPORTER_ASSERT(r, 0 == buffer.size());
+}