Fix an incorrect iteration with a workList (shader-slang#6177)

* Fix an incorrect iteration with a workList

We cannot modify workList while iterating it, because its type `List` is
actually an array container.

* Change based on the feedback

* Use `Index` instead of `int` for for-loop index

---------

Co-authored-by: Yong He <yonghe@outlook.com>

Author: jkwak-work

source/slang/slang-ir-variable-scope-correction.cpp

@@ -121,11 +121,12 @@ void VariableScopeCorrectionContext::_processFunction(IRFunc* funcInst)
 
     auto instAfterParam = funcInst->getFirstBlock()->getFirstOrdinaryInst();
 
-    for (auto inst = workList.begin(); inst != workList.end(); inst++)
+    for (Index i = 0; i < workList.getCount(); i++)
     {
-        if (auto loopHeaderList = loopHeaderMap.tryGetValue(getBlock(*inst)))
+        auto inst = workList[i];
+        if (auto loopHeaderList = loopHeaderMap.tryGetValue(getBlock(inst)))
         {
-            _processInstruction(dominatorTree, instAfterParam, *inst, *loopHeaderList, workList);
+            _processInstruction(dominatorTree, instAfterParam, inst, *loopHeaderList, workList);
         }
     }
 }