Set default for share_embeddings_and_output_weights (#4569)

Signed-off-by: chochowski <mchochowski@nvidia.com>

Author: chochowski

src/megatron/bridge/models/conversion/model_bridge.py

@@ -1490,7 +1490,7 @@ def _share_embeddings_and_output_weights(
         model_config: TransformerConfig,
     ) -> bool:
         """Shared embedding setting."""
-        return getattr(model_config, "share_embeddings_and_output_weights")
+        return getattr(model_config, "share_embeddings_and_output_weights", False)
 
     def _unwrap_name(self, name: str) -> str:
         """Unwrap name from DDP or other wrappers.