Add missing length check when copying fixed arrays.

src/heap-inl.h

Index: src/heap-inl.h
diff --git a/src/heap-inl.h b/src/heap-inl.h
index 4f92d0882fc9ffbddf08d0e074e33a67c52e85d7..a728777df19b9b93d196320807fa56118d60991a 100644
--- a/src/heap-inl.h
+++ b/src/heap-inl.h
@@ -161,16 +161,19 @@ MaybeObject* Heap::AllocateTwoByteInternalizedString(Vector<const uc16> str,
 }
 
 MaybeObject* Heap::CopyFixedArray(FixedArray* src) {
+  if (src->length() == 0) return src;
   return CopyFixedArrayWithMap(src, src->map());
 }
 
 
 MaybeObject* Heap::CopyFixedDoubleArray(FixedDoubleArray* src) {
+  if (src->length() == 0) return src;
   return CopyFixedDoubleArrayWithMap(src, src->map());
 }
 
 
 MaybeObject* Heap::CopyConstantPoolArray(ConstantPoolArray* src) {
+  if (src->length() == 0) return src;
   return CopyConstantPoolArrayWithMap(src, src->map());
 }