Joshuto exits with error on "open_with" action attempt without a target

[steven-reina]

Description:

Using joshuto, when attempting to open an empty target (on an empty directory) with an arbitrary command (using the native :open_with command), it perhaps handles this error case by exiting joshuto altogether, with a 101 exit code.
This error is reproducible, regardless of the platform it's run on.

System information:

• OS: Arch Linux / macOS Sonoma 14.5
• Kernel: Linux 6.9.4-arch1-1 / Darwin 23.5.0
• Software version: joshuto-0.9.8

How to reproduce:

• Enter an empty directory
• Execute Joshuto's native command :open_with (or hit r, which is the default shortcut)
• Joshuto terminates with exit code 101

Expectation:

I don't believe this to be the intended way to handle such case, so it should simply print some warning in the information/command bar, or maybe nothing at all, as is the case for the :open command under the same circumstances, as of right now.