Add missing 'else' at JwtSecurityTokenHandler.cs:1384 so that IssuerS…

[fre-berhane]

Fix missing else keyword in JwtSecurityTokenHandler key resolution

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Summary of the changes (Less than 80 chars)

Description

Add missing 'else' at JwtSecurityTokenHandler.cs:1384 so that IssuerSigningKeyResolverUsingConfiguration takes priority over IssuerSigningKeyResolver and default kid-based resolution, matching the documented contract and the correct behavior already present in JsonWebTokenHandler.

Fixes #{bug number} (in this specific format)