Guard local time posix functions from NaN value of invalid dates.

src/platform-nullos.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 62 matching lines @@
 
 // Returns ticks in microsecond resolution.
 int64_t OS::Ticks() {
   UNIMPLEMENTED();
   return 0;
 }
 
 
 // Returns a string identifying the current timezone taking into
 // account daylight saving.
-char* OS::LocalTimezone(double time) {
+const char* OS::LocalTimezone(double time) {
   UNIMPLEMENTED();
   return "<none>";
 }
 
 
 // Returns the daylight savings offset in milliseconds for the given time.
 double OS::DaylightSavingsOffset(double time) {
   UNIMPLEMENTED();
   return 0;
 }
@@ skipping 333 matching lines @@
 }
 
 
 void ProfileSampler::Stop() {
   UNIMPLEMENTED();
 }
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal