glib: Document G_IO_ERROR as a possible error condition

This was already implicit from G_IO_ERROR_NOT_SUPPORTED being a
documented error condition, and from the use of GCancellable, but is
probably clearer when spelled out explicitly. The addition of
g_seekable_seek() and g_seekable_tell() in the previous commit might
add more error conditions in the same domain.

Signed-off-by: Simon McVittie <smcv@debian.org>
diff --git a/glib/poppler-document.cc b/glib/poppler-document.cc
index fdaa8b0..49c9ed3 100644
--- a/glib/poppler-document.cc
+++ b/glib/poppler-document.cc
@@ -276,8 +276,8 @@
  * Creates a new #PopplerDocument reading the PDF contents from @stream.
  * Note that the given #GInputStream must be seekable or %G_IO_ERROR_NOT_SUPPORTED
  * will be returned.
- * Possible errors include those in the #POPPLER_ERROR and #G_FILE_ERROR
- * domains.
+ * Possible errors include those in the #POPPLER_ERROR, #G_FILE_ERROR
+ * and #G_IO_ERROR domains.
  *
  * Returns: (transfer full): a new #PopplerDocument, or %NULL
  *