Fix Regression in Model PSS and PSR, add check for zero-size initializers

[intbf]

Description

In #817 we assumed that initializers's size is larger than zero. This is not the case for some models. While Initializers with RAW data usually works, as OV can skip them, there was an issue when we converted those initializers with RAW data to initializers with EXT data in memory.
So it's safe to add this check on the OVEP side (later we'll try to improve OpenVino side as well, and double check with their implementation)

Motivation and Context

CVS-174653

[MayureshV1]

LGTM !

[Copilot]

Pull Request Overview

This PR fixes a regression in model PSS and PSR by adding a safety check for zero-size initializers before calling SetExternalDataFields. Previously, the code assumed all initializers had non-zero size, but some models contain empty initializers that caused issues when converting RAW data to EXT data in memory.

• Added size validation check before calling SetExternalDataFields
• Added verbose logging for empty initializers that are skipped
• Prevents issues with zero-size initializers in OpenVino execution provider

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