Fix another may not be init compile error on AIX

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 83fb6394f96e500027120929fbe70b93a438209b..8122e07ea1cd29faa0676cbf25d0c4a4bb4f5e7f 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2416,7 +2416,7 @@ void Heap::ConfigureInitialOldGenerationSize() {
 
 AllocationResult Heap::AllocatePartialMap(InstanceType instance_type,
                                           int instance_size) {
-  Object* result;
+  Object* result = nullptr;
   AllocationResult allocation = AllocateRaw(Map::kSize, MAP_SPACE, MAP_SPACE);
   if (!allocation.To(&result)) return allocation;