Fix --private and others showing weird error when used without argument

[ghost]

When using some of the options like --private without an argument, which shouldn't be done but users make mistakes sometimes, this currently causes a weird backtrace error that isn't obvious to the average user. This pull request addresses that problem such that better error handling can happen

[homdx]

Very good!!! @Jonast , thank you !

checked in added link
#1570 (comment)

[inclement]

I guess I also missed that this should really also check if the i+1th entry is also an argument (starting with - or --) before converting it to a path.

[ghost]

@inclement argparse supports -- though after which - in front of a path is allowed. So this might break legitimate path arguments if that's not taken into account... could make things complicated

[inclement]

@Jonast Sure, it's not that we need to reinvent the argparse logic so much as that it would probably improve more errors than it makes worse.