Don't crash if the tm_zone field returned by localtime is NULL

src/base/platform/platform-linux.cc

 // Copyright 2012 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.
 
 // Platform-specific code for Linux goes here. For the POSIX-compatible
 // parts, the implementation is in platform-posix.cc.
 
 #include <pthread.h>
 #include <semaphore.h>
 #include <signal.h>
@@ skipping 91 matching lines @@
 
 
 const char* OS::LocalTimezone(double time, TimezoneCache* cache) {
 #if V8_OS_NACL
   // Missing support for tm_zone field.
   return "";
 #else
   if (std::isnan(time)) return "";
   time_t tv = static_cast<time_t>(std::floor(time/msPerSecond));
   struct tm* t = localtime(&tv);
-  if (NULL == t) return "";
+  if (!t || !t->tm_zone) return "";
   return t->tm_zone;
 #endif
 }
 
 
 double OS::LocalTimeOffset(TimezoneCache* cache) {
 #if V8_OS_NACL
   // Missing support for tm_zone field.
   return 0;
 #else
@@ skipping 314 matching lines @@
 #endif
   return munmap(base, size) == 0;
 }
 
 
 bool VirtualMemory::HasLazyCommits() {
   return true;
 }
 
 } }  // namespace v8::base