nautils-search-engine-tracker: Only parse non-null dates

Fix critical when parsing null date string:

GLib-CRITICAL **: 12:05:52.144: g_time_val_from_iso8601: assertion 'iso_date != NULL' failed

This is possible since tracker can return NULL[1] "if the column is
not in the [0,#ncolumns] range"

[1] https://gnome.pages.gitlab.gnome.org/tracker/docs/developer/tracker-sparql-cursor.html?gi-language=c#tracker_sparql_cursor_get_string

1 files changed, 16 insertions, 7 deletions

diff --git a/src/nautilus-search-engine-tracker.c b/src/nautilus-search-engine-tracker.c
index 51917216b..bafc8148b 100644
--- a/src/nautilus-search-engine-tracker.c
+++ b/src/nautilus-search-engine-tracker.c
@@ -181,7 +181,7 @@ cursor_callback (GObject      *object,
     const char *atime_str;
     const char *ctime_str;
     const gchar *snippet;
-    GDateTime *date;
+    GDateTime *date = NULL;
     g_autoptr (GTimeZone) tz = g_time_zone_new_local ();
     gdouble rank, match;
     gboolean success;
@@ -232,31 +232,40 @@ cursor_callback (GObject      *object,
         }
     }
 
-    date = g_date_time_new_from_iso8601 (mtime_str, tz);
+    if (mtime_str != NULL)
+    {
+        date = g_date_time_new_from_iso8601 (mtime_str, tz);
+    }
     if (date != NULL)
     {
         nautilus_search_hit_set_modification_time (hit, date);
-        g_date_time_unref (date);
+        g_clear_pointer (&date, g_date_time_unref);
     }
     else
     {
         g_warning ("unable to parse mtime: %s", mtime_str);
     }
-    date = g_date_time_new_from_iso8601 (atime_str, tz);
+    if (atime_str != NULL)
+    {
+        date = g_date_time_new_from_iso8601 (atime_str, tz);
+    }
     if (date != NULL)
     {
         nautilus_search_hit_set_access_time (hit, date);
-        g_date_time_unref (date);
+        g_clear_pointer (&date, g_date_time_unref);
     }
     else
     {
         g_warning ("unable to parse atime: %s", atime_str);
     }
-    date = g_date_time_new_from_iso8601 (ctime_str, tz);
+    if (ctime_str != NULL)
+    {
+        date = g_date_time_new_from_iso8601 (ctime_str, tz);
+    }
     if (date != NULL)
     {
         nautilus_search_hit_set_creation_time (hit, date);
-        g_date_time_unref (date);
+        g_clear_pointer (&date, g_date_time_unref);
     }
     else
     {