[PATCH] notmuch-dump.c: Fix output file being closed twice

[David Bremner]

Ralph Seichter <abbot at monksofcool.net> writes:

> Fixed: If the output file for a dump was non-writeable, gzclose_w()
> was called twice on the output file handle, resulting in SIGABRT.

LGTM, although I did have to revert one unrelated whitespace change.

I'll push that later if no-one objects.

d