Fix assert for lastDefBeforeFirstUse

Summary:
An assert was incorrectly computing the last def before first use, causing false assert failures.

#utd-hermes-ignore-wasm

Reviewed By: dulinriley

Differential Revision: D26695876

fbshipit-source-id: 1d81b54dc97e46bb48a9b3d5d8a18000d664411f

API/hermes/TraceInterpreter.cpp

@@ -311,7 +311,7 @@ std::unordered_map<ObjectID, TraceInterpreter::DefAndUse> createGlobalMap(
         defs.size() &&
         "There must be at least one def for any globally used object");
     // The defs here are global record numbers.
-    uint64_t lastDefBeforeFirstUse = *defs.begin();
+    uint64_t lastDefBeforeFirstUse = 0;
     for (uint64_t def : defs) {
       if (def < firstUse) {
         lastDefBeforeFirstUse = std::max(lastDefBeforeFirstUse, def);