- press pick plugin key
- navigate away from the plugin directory (to ~, say)
- try to open any file, fails

When we are in run plugin mode, but detect we are in a different
context or a non-plugin directory, just cancel the runplgin mode
and continue as usual.

It also cleans up the plugin run function.

xargs couldn't call function `dnd()` and I couldn't find a portable way
to do it, so I replaced it with a variable which I guess should work
fine.

For w/e reason the output from `which` causes problems with nnn
rendering. This commit silences the problematic lines.