Fix a SEGV in the register allocator....

src/lithium-allocator.cc

 // Copyright 2010 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 508 matching lines @@
   UseInterval* a = FirstSearchIntervalForPosition(b->start());
   while (a != NULL && b != NULL) {
     if (a->start().Value() > other->End().Value()) break;
     if (b->start().Value() > End().Value()) break;
     LifetimePosition cur_intersection = a->Intersect(b);
     if (cur_intersection.IsValid()) {
       return cur_intersection;
     }
     if (a->start().Value() < b->start().Value()) {
       a = a->next();
-      if (a == NULL && a->start().Value() > other->End().Value()) break;
+      if (a == NULL || a->start().Value() > other->End().Value()) break;
       AdvanceLastProcessedMarker(a, advance_last_processed_up_to);
     } else {
       b = b->next();
     }
   }
   return LifetimePosition::Invalid();
 }
 
 
 void LAllocator::InitializeLivenessAnalysis() {
@@ skipping 1567 matching lines @@
     LiveRange* current = live_ranges()->at(i);
     if (current != NULL) current->Verify();
   }
 }
 
 
 #endif
 
 
 } }  // namespace v8::internal