Merge pull request #68187 from al45tair/eng/PR-114447171

[Demangling] Avoid UB call to memcpy().

Author: al45tair

include/swift/Demangling/Demangler.h

@@ -206,7 +206,8 @@ class NodeFactory {
     if (Growth < Capacity * 2)
       Growth = Capacity * 2;
     T *NewObjects = Allocate<T>(Capacity + Growth);
-    memcpy(NewObjects, Objects, OldAllocSize);
+    if (OldAllocSize)
+      memcpy(NewObjects, Objects, OldAllocSize);
     Objects = NewObjects;
     Capacity += Growth;
   }