fail to run if only dir is specified and not config file full path

[MarnixCroes]

In case a specified config file does not exist it should fail to run.
Currently it logs Using config file: "x", even when x is not a config file.

for example, when running ./bs --config=/home/user/Documents

[MarnixCroes]

This is when you enter a dir, instead of non existing config file.

[evoskuil]

With existing directory this is what I get in Windwos.

> bs -c m:/foo
Error: can not read options configuration file 'm:\foo'

[evoskuil]

Requires more info, @eynhaender can you verify?