[glib] gdesktopappinfo: Mark GDesktopAppInfo constructors as nullable.

[Philip Withnall <pwithnall src gnome org>]

commit 9d40f64960dbe7e5cd0eb24c5427a4dc30623e35
Author: Tomasz Miąsko <tomasz miasko gmail com>
Date:   Fri May 4 00:00:00 2018 +0000

    gdesktopappinfo: Mark GDesktopAppInfo constructors as nullable.
    
    GDesktopAppInfo constructors return NULL on error without having
    separate **GError parameter.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=795152

 gio/gdesktopappinfo.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/gio/gdesktopappinfo.c b/gio/gdesktopappinfo.c
index 6844ff330..a2aa760c7 100644
--- a/gio/gdesktopappinfo.c
+++ b/gio/gdesktopappinfo.c
@@ -1858,7 +1858,7 @@ g_desktop_app_info_load_file (GDesktopAppInfo *self)
  *
  * Creates a new #GDesktopAppInfo.
  *
- * Returns: a new #GDesktopAppInfo or %NULL on error.
+ * Returns: (nullable): a new #GDesktopAppInfo or %NULL on error.
  *
  * Since: 2.18
  **/
@@ -1884,7 +1884,7 @@ g_desktop_app_info_new_from_keyfile (GKeyFile *key_file)
  *
  * Creates a new #GDesktopAppInfo.
  *
- * Returns: a new #GDesktopAppInfo or %NULL on error.
+ * Returns: (nullable): a new #GDesktopAppInfo or %NULL on error.
  **/
 GDesktopAppInfo *
 g_desktop_app_info_new_from_filename (const char *filename)
@@ -1916,7 +1916,8 @@ g_desktop_app_info_new_from_filename (const char *filename)
  * (i.e. a desktop id of kde-foo.desktop will match
  * `/usr/share/applications/kde/foo.desktop`).
  *
- * Returns: a new #GDesktopAppInfo, or %NULL if no desktop file with that id
+ * Returns: (nullable): a new #GDesktopAppInfo, or %NULL if no desktop
+ *     file with that id exists.
  */
 GDesktopAppInfo *
 g_desktop_app_info_new (const char *desktop_id)