cxx helpers: shared_data: Add nullptr comparison operators

Signed-off-by: Thomas Guillem <thomas@gllm.fr>

include/vlc_cxx_helpers.hpp

@@ -202,11 +202,21 @@ public:
         return ptr == other.ptr;
     }
 
+    bool operator==(std::nullptr_t) const noexcept
+    {
+        return ptr == nullptr;
+    }
+
     bool operator!=(const vlc_shared_data_ptr &other) const
     {
         return !(*this == other);
     }
 
+    bool operator!=(std::nullptr_t) const noexcept
+    {
+        return ptr != nullptr;
+    }
+
     explicit operator bool() const
     {
         return ptr;