avoid validation of existing providers

[kjgarza]

Purpose

Validation of provider check if the symbol is unique even when the provider is being updated. This causes an error on updating providers.

closes: #463

Approach

Avoid validation of uniqueness for existent records.

Learning

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• New feature (non-breaking change which adds functionality)

• Breaking change (fix or feature that would cause existing functionality to change)

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[mfenner]

LGTM