Fix "Testable Files" file extension comparison

Issue introduced in v3.19: Testable Files (a.k.a. upload processors) with a specified file extension/type (e.g. "ZIP" and not "*") would never run because the file extension comparison logic was "off by one". Testable Files with an extension of "*" (all files/types) would still run however.

This fixes issue #331 reported by Nightfox.