Check that a valid RawVarData has been created before calling a function on it

ppapi/proxy/raw_var_data.cc

Index: ppapi/proxy/raw_var_data.cc
diff --git a/ppapi/proxy/raw_var_data.cc b/ppapi/proxy/raw_var_data.cc
index 9dbd75bcf3ff91fb7dbeea24b440b9c89569148f..117e35672f7b83b41126645b6180f1975e138230 100644
--- a/ppapi/proxy/raw_var_data.cc
+++ b/ppapi/proxy/raw_var_data.cc
@@ -198,6 +198,8 @@ std::unique_ptr<RawVarDataGraph> RawVarDataGraph::Read(
       return nullptr;
     PP_VarType var_type = static_cast<PP_VarType>(type);
     result->data_.push_back(base::WrapUnique(RawVarData::Create(var_type)));
+    if (!result->data_.back())
+      return nullptr;
     if (!result->data_.back()->Read(var_type, m, iter))
       return nullptr;
   }