template: Not erroring when download fails

[obiwac]

This obviously should error straight away instead of just saying "Finished":

root@:/tmp # aquarium -r /tmp/aquariums -c linux -t amd64.ubuntu.focal
Found template, downloading from https://github.com/inobulles/bob-linux-images/releases/download/amd64.ubuntu.focal/amd64.ubuntu.focal.txz ...
Finished
aquarium: Total size of downloaded template (20971520 bytes) is not the size expected (123438644 bytes). Someone may be trying to swindle you!
root@:/tmp # fetch https://github.com/inobulles/bob-linux-images/releases/download/amd64.ubuntu.focal/amd64.ubuntu.focal.txz
amd64.ubuntu.focal.txz                         16% of  117 MB 7696 kBps    14s
fetch: amd64.ubuntu.focal.txz: No space left on device
root@:/tmp #