Building in a wrong folder results in weird errors about unrelated programs

Expected Behavior

When doing a build while specifying a wrong relative path to a Dockerfile, the error output should say something about that file not being found instead of a totally unrelated program.

This is the command that I used:
sudo docker-slim build --http-probe=false --dockerfile containers/base/Dockerfile --tag lalalala.dkr.ecr.us-east-2.amazonaws.com/smalltest --mount /var/run/docker.sock:/var/run/docker.sock --mount /usr/bin/docker:/usr/bin/docker --show-clogs --entrypoint "entrypoint_dockerslim" .

Actual Behavior

During build, this error popped up and stops the build:

cmd=build info=build.error status=standard.image.build.error value='cannot open "/home/thesheeep/.config/copyq/.copyq_s" for reading: open /home/thesheeep/.config/copyq/.copyq_s: no such device or address'

The error that I got was so weird and confusing ("wtf does CopyQ have to do with anything?!") that it took me quite a while to figure out what was actually the problem.
The actual problem here was that I ran the command above in my home folder (I was just silly and forgot to cd to the correct folder beforehand), so obviously there is no <home>/containers/base/Dockerfile.
If docker-slim had just flat out told me "The Dockerfile you specified could not be found" or something similar, I could have done my facepalm much earlier.

Maybe a sanity check of all the arguments passed would be in order just to improve error output for sleepyheads like myself a bit 🤣

Specifications

• Version: docker-slim version linux|Transformer|1.34.0-16-gdc85082|dc85082121a8abf5c3984668b8a0c87d3fd7a51a|2021-02-16_07:58:23AM
• Platform: Manjaro Linux

Reproduce the docker-slim build command from an incorrect working directory with the relative Dockerfile path shown. Trace the build entry point until the path is handled, then make the failure identify the missing Dockerfile instead of reporting an unrelated file; verify the resulting error with the same command.