Fix two-char hash to use correct fallback for zero hashes.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 037e460c3f86ea4cb063b277c419e9342459e666..e3fcb93a7589c8e0603fb26cf6824d95ad088641 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -2713,7 +2713,7 @@ bool Heap::CreateInitialObjects() {
   // hash code in place. The hash code for the hidden_symbol is zero to ensure
   // that it will always be at the first entry in property descriptors.
   { MaybeObject* maybe_obj =
-        AllocateSymbol(CStrVector(""), 0, String::kZeroHash);
+        AllocateSymbol(CStrVector(""), 0, String::kEmptyStringHash);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   hidden_symbol_ = String::cast(obj);