glib: Don't create PopplerInputStream with length 0

Since commit a59f6164, PopplerInputStream requires a nonzero length.

Loosely based on an earlier patch by Kouhei Sutou. This version adds
support for length == -1, which is documented to work.

Resolves: https://gitlab.freedesktop.org/poppler/poppler/issues/414
Bug-Debian: https://bugs.debian.org/896596
1 file changed