Fixing PreFast error

lib/common/Memory/CustomHeap.h

@@ -301,7 +301,7 @@ public:
         return page->HasNoSpace() || (allocXdata && !((Segment*)(page->segment))->CanAllocSecondary());
     }
 
-    BOOL ProtectAllocation(__in Allocation* allocation, DWORD dwVirtualProtectFlags, DWORD desiredOldProtectFlag, __in char* addressInPage = nullptr);
+    BOOL ProtectAllocation(__in Allocation* allocation, DWORD dwVirtualProtectFlags, DWORD desiredOldProtectFlag, __in_opt char* addressInPage = nullptr);
     BOOL ProtectAllocationWithExecuteReadWrite(Allocation *allocation, char* addressInPage = nullptr);
     BOOL ProtectAllocationWithExecuteReadOnly(Allocation *allocation, char* addressInPage = nullptr);