internal/cuetxtar: print error details
Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: Icae33ba347e74ead2b3302c0801e555adc2e891f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/553112
Reviewed-by: Marcel van Lohuizen <mpvl@gmail.com>
Unity-Result: CUEcueckoo <cueckoo@cuelang.org>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>