Don't cd into wrong directories

The path in a local variable wasn't properly updated, that's why vifm
did try to cd into a directory even after determining there will be
issues with it.
Simplify interface of the leave_invalid_dir() func

Removed the second parameter of the function.
Update comment of the leave_invalid_dir() function

Add general description.
Document cd'ing to a wrong directory fix
Merge branch 'fix-cd-on-dir-access-error'