dir_import.c: Various fixes
dir_import.c: Various fixes

- errors in item() didn't propagate properly
- empty [] and {} values weren't allowed
- fractional numbers weren't allowed
- parsing of escaped characters didn't ensure that enough data was in
  the buffer
- E() didn't propagate errors properly in all cases

I'll do some more testing later on, but the current code seems to be
working quite well already.

rofl0r/ncdu,piyo/ncdu,guns/ncdu,guns/ncdu,FauxFaux/ncdu,FauxFaux/ncdu,gitkaste/ncdu,sunny256/ncdu,sunny256/ncdu,gitkaste/ncdu,guns/ncdu,ppetr/ncdu,ppetr/ncdu,ppetr/ncdu,rofl0r/ncdu