Fix initializer load for in-memory external data

[tairenpiao]

Description

The Initializer(graph, …) constructor wrongly required a model_path for an initializer with in-memory external data when its OrtValue wasn't registered. It now loads the data from memory via CreateTensorFromTensorProto, matching the other constructor.

Motivation and Context

Fixes #28267. A model loaded from bytes via CreateSessionFromArray failed with model_path must not be empty; loading the same model from a file worked.

[Copilot]

Pull request overview

Fixes Initializer(graph, ...) behavior for initializers that use in-memory external data when the corresponding OrtValue is not registered: the constructor no longer incorrectly requires a non-empty model_path, and instead falls back to CreateTensorFromTensorProto to load from the in-memory external buffer (consistent with the other Initializer constructor). This addresses the CreateSessionFromArray failure reported in #28267.

Changes:

• Remove the model_path must not be empty enforcement in the graph-based Initializer constructor for the in-memory-external-data + missing-OrtValue case.
• Add a regression test covering an in-memory external-data initializer with empty model_path and no registered OrtValue.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
onnxruntime/core/optimizer/initializer.cc	Removes the incorrect model_path enforcement so in-memory external data can be loaded via CreateTensorFromTensorProto when no OrtValue is present.
onnxruntime/test/optimizer/initializer_test.cc	Adds a regression test to ensure in-memory external-data initializers load correctly without model_path when no OrtValue is registered.