[wasm] Fix decoder for null data

src/wasm/decoder.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_DECODER_H_
 #define V8_WASM_DECODER_H_
 
 #include <memory>
 
 #include "src/base/compiler-specific.h"
@@ skipping 235 matching lines @@
     }
     TRACE("<end>\n");
     pc_ = limit_;
     return t;
   }
 
   // Converts the given value to a {Result}, copying the error if necessary.
   template <typename T>
   Result<T> toResult(T val) {
     Result<T> result;
-    if (error_pc_) {
+    if (failed()) {
       TRACE("Result error: %s\n", error_msg_.get());
       result.error_code = kError;
       result.start = start_;
       result.error_pc = error_pc_;
       result.error_pt = error_pt_;
       // transfer ownership of the error to the result.
       result.error_msg.reset(error_msg_.release());
     } else {
       result.error_code = kSuccess;
     }
     result.val = std::move(val);
     return result;
   }
 
   // Resets the boundaries of this decoder.
   void Reset(const byte* start, const byte* end) {
     start_ = start;
     pc_ = start;
     limit_ = end;
     end_ = end;
     error_pc_ = nullptr;
     error_pt_ = nullptr;
     error_msg_.reset();
   }
 
-  bool ok() const { return error_pc_ == nullptr; }
-  bool failed() const { return !!error_msg_; }
+  bool ok() const { return error_msg_ == nullptr; }
+  bool failed() const { return !ok(); }
   bool more() const { return pc_ < limit_; }
 
   const byte* start() { return start_; }
   const byte* pc() { return pc_; }
   uint32_t pc_offset() { return static_cast<uint32_t>(pc_ - start_); }
 
  protected:
   const byte* start_;
   const byte* pc_;
   const byte* limit_;
@@ skipping 97 matching lines @@
     return traceOffEnd<uint32_t>();
   }
 };
 
 #undef TRACE
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_DECODER_H_