[tracker] tracker-miner-fs: avoid crash during init

[David King <davidk src gnome org>]

commit 531947327ff00a82a91d99430fbfb757eac5d4a5
Author: David King <amigadave amigadave com>
Date:   Tue Aug 25 10:28:34 2015 +0100

    tracker-miner-fs: avoid crash during init
    
    Correctly handle the result of tracker_sparql_cursor_get_string(), which
    can be NULL.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=754055

 src/miners/fs/tracker-miner-files.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/miners/fs/tracker-miner-files.c b/src/miners/fs/tracker-miner-files.c
index fb7445f..527c6e5 100644
--- a/src/miners/fs/tracker-miner-files.c
+++ b/src/miners/fs/tracker-miner-files.c
@@ -929,6 +929,9 @@ init_mount_points (TrackerMinerFiles *miner_files)
 
                urn = tracker_sparql_cursor_get_string (cursor, 0, NULL);
 
+               if (!urn)
+                       continue;
+
                if (strcmp (urn, TRACKER_DATASOURCE_URN_NON_REMOVABLE_MEDIA) == 0) {
                        /* Report non-removable media to be mounted by HAL as well */
                        state |= VOLUME_MOUNTED;