uru4000: Don't force encryption detection on UrU4000B

The output of the UrU4500 device isn't always encrypted, so try to
process it as an unencrypted image before falling back.

See d003f088
1 job from wip/hadess/uru4500-autodetect-encryption in 3 minutes and 25 seconds (queued for 1 minute and 50 seconds)
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passed #19878
build

00:03:25