globbing: fix crash on unballanced open brace

Having an open brace without a closing brace caused a segfault.

Having a closing brace too many caused a silent error to occur, which
caused curl to bail out and return an error code but no error message
was shown. It does now!

All error message outputs no longer wrongly get _two_ newlines written
after the error message.

Reported by: Vlad Ureche
Bug: http://curl.haxx.se/bug/view.cgi?id=3083942