Handle reading byte past the end of file

runtime/bin/file.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/file.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 
 #include "include/dart_api.h"
@@ skipping 67 matching lines @@
 
 void FUNCTION_NAME(File_ReadByte)(Dart_NativeArguments args) {
   Dart_EnterScope();
   intptr_t return_value = -1;
   intptr_t value =
       DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 0));
   File* file = reinterpret_cast<File*>(value);
   if (file != NULL) {
     uint8_t buffer;
     int bytes_read = file->Read(reinterpret_cast<void*>(&buffer), 1);
-    if (bytes_read >= 0) {
+    if (bytes_read == 1) {
       return_value = static_cast<intptr_t>(buffer);
+    } else {
+      return_value = -1;
     }
   }
   Dart_SetReturnValue(args, Dart_NewInteger(return_value));
   Dart_ExitScope();
 }
 
 
 void FUNCTION_NAME(File_WriteByte)(Dart_NativeArguments args) {
   Dart_EnterScope();
   intptr_t return_value = -1;
@@ skipping 201 matching lines @@
   Dart_EnterScope();
   const char* str =
       DartUtils::GetStringValue(Dart_GetNativeArgument(args, 0));
   char* path = File::GetCanonicalPath(str);
   if (path != NULL) {
     Dart_SetReturnValue(args, Dart_NewString(path));
     free(path);
   }
   Dart_ExitScope();
 }