Empty MBE window when changing working directory

[dezull]

I'm bringing the old issue from fholgado/minibufexpl.vim#119, I don't think it has been resolved yet.

I may have found the reason, where at various places this check is performed:

    if bufname('%') != '-MiniBufExplorer-'

to validate the window is indeed MBE's window. Initially that is fine as the bufname matches '-MiniBufExplorer-' exactly.

But after a directory change, it changes to something like:

    /<some-paths...>/.vim_runtime/-MiniBufExplorer-

We can use:

    if bufname('%') !~ '-MiniBufExplorer-'

unless a file with that name exists in that directory, do you think that is ok?

[dezull]

I've made a PR #47 so I'm closing this.